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J.L.S.B. LVI]
TRANSFERENCE OF BUNCTION
33
TRANSFERENCE OF FUNCTION
By E. J. H. CORNER,F.R.S.
(Botany School, Cambridge.)
(With 2 text-figures.)
The systematic comparison of plants, and probably of animals, shows that a
property which occurs in an organ, tissue, or cell-layer in one case may occur in other
parts of the body in other cases. The property is the same, but its site of development
has shifted. These deviations are found a t all levels of classification ; the transference
of function, therefore, as I have called the process (Corner, 1949a, p. 381 ; 19496,
p. 360) is a method of evolution.
A simple example is the presence of anthocyanin in the flowering-plant. At some
stage in development, the colour appears. In one variety the underside of the leaf
may be red, or merely the veins, or the petiole or node or internode, or the colour may
appear only in young leaves or old leaves, or only on insolated surfaces. Such small
differences are usually passed over, though of horticultural value ; yet, they raise
the question why one part of the epidermis should be different from another. There
is not just the property to be considered, but the site of its materialization. Presumably the property is inherent in all the cells, but only in certain parts of the body
do the circumstances evoke it. A hereditary character consists of two parts, the property and, what must be more complex, the conditions which materialize it. Thus I
understand the evolution of the property as anagenesis in the fist place, and the
diversification or cladogenesis of its occurrence. Stasigenesis of Huxley (1957) is
shown by the widespread pigmentation of petals rather than sepals. When, with the
loss of petals, the calyx becomes pigmented, there is a profound modification of floral
organization, as Miss Saunders (1033) has explained. A remarkable instance is
Sairaca (Leguminosae-Caesalpinioideae-Amherstieae).Its petals are lost ; the tetramerous calyx takes their function and their vascular supply ; the inner whorl of
stamens takes the place of the petals ; and the outer whorl of stamens is variously
reduced (Text-fig. 1). S. thaipingensis Cantley ex King has the effective formula K4
CO A 0 4,but the full vascular supply K5 C5 A5 5, the petal-bundles lying in the
sepals and the bundles of the undeveloped stamens ending blindly in the receptacle
(Rao & Sirdeshmukh, 1954). The derivation of this flower can be traced through other
species and such allied genera as Pahudia, in which the four petals, other than the
standard, soon abort and the inner stamens encroach upon their positions. There
is no metaphysical problem whether sepals are homologous with petals or petals with
stamens or whether any of them are defined by vascular bundles ; indeed, there is
nothing new in this flower but the transference of function from one part to another
and degeneration characteristic of the zygomorphy of the tribe. Yet, the transference
of colour is here the outward sign of intensive evolution.
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Floral Examples.
Most cruciferous inflorescences have no bracts, save at the beginning of the raceme.
The bracts can be traced on the stem-apex as inhibited leaves. As the inflorescence
develops, the inhibition increases ; the flower-primordia occur a t first in the axils
of microscopic bracts, and then the primordia which should become bracts become
flower-buds directly. That is, the stem- (inflorescence-)apex produces in phyllotaxis
not leaves (bracts) but stems (flower-buds) without attendant leaves. Here, again,
there is no metaphysical problem such as whether a phyllome-system is turning into
a telome-system or a cruciferous inflorescence is not homologous with a vegetative
shoot, but a direct and observable transference of the properties of engendering a
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[J.L.s.z. XLIV,
E. J. H. CORNER:
flower-bud from the axillary position to the primary primordial position. I write
observable because it can be seen in a few minutes on dissecting the young inflorescence
of Cupselfa under the binocular microscope, which I take as my first practical in
advanced taxonomy ; i t is not in the books. Nevertheless, the same process must
occur in composite capitula and aroid spadices without interfloral bracts, though so
subtly as scarcely to excite remark. The process must be the explanation, a t least in
part, of the notable epiphyllous flowers borne on mid-ribs (Stork, 1956).
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TEXT-FIG.
1.-Leguminosae- Caesalpinioideae- Amherstieae.
Flower-buds showing the primordia of petals, stamens and ovary (central),the sepals cut off but
numbered in order of development (2 and 5 connate), x 50.
Sections of full-grown flower-buds a t the level of insertion of the sepals to show the sepal w.b.
(black), the petal w.b. and their sepaline derivatives (white), the stamina1 w.b. (dotted),
and the ovary w.b. (hatched), X 15.
A , B, Hymenaea courbaril L. (K4 C5 A5
5) : c , Pahudia rhomboidea Prain (K4 C1 A3
4) : D,
Saraca declinata Miq. (K4 CO A3
4) : E , F, Saraca thaipingensis Cantley ex King (K4
CO A 0 + 4) ; the inner whorl of stamens (i).
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Condensed inflorescences simulate single flowers. Outer bracts resemble sepals,
inner bracts or neuter flowers petals, male flowers stamens, and central fruiting
florets carpels. Such inflorescences are condensed because there is no internodal
extension (that of the female flower in Euphorbia simulating the gynophore), and on
the broadened inflorescence-apex the many small flowers are crowded. It is under
J.L.S.B. LVI]
TRANSFERENCE OF FUNCTlON
35
conditions of complicated proximity that transference of function is to be expected ;
the circumstances under which properties materialize are there likely to overlap.
There is, again, no need to appeal to a metaphysical floral " Gestalt ", but to perceive
the way in which floral properties precociously pervade the stem-apex co-extensively
with inflorescence properties. Such inflorescence-flowers, in fact, affirm the floral
properties by transferring them to the greater scale of the inflorescence. A precise
example is afforded by Parkia (Leguminosae-Mimosoideae). I n the Amazonian
section Paryphosphaera (Ducke, 1938), the large clavate capitulum has sterile, petaloid
basal flowers, then many functional male flowers, and about a dozen apical perfect
flowers which set individual pods. The compound fruit of Parkia resembles in its
inflorescence-stalk, head, and bunch of pods the simple fruit of Awhidendron, of the
same subfamily, where the pods are from the numerous carpels of the one flower.
A r c ~ i ~ e n d r ohas
n simpIe capitula without transference of floral properties, but
Pentaclethra, allied with Parkia, with petaloid stamens is in some measure intermediate;
i t shows how the steps in cladogenesis may be revealed by allied genera.
The syncarpous ovary has always been a problem, now beset with many artificial
theories. I n essence it is an intercalary growth a t the base of the free or apocarpous
carpel-primordia, which thus become elevated on the new " ovary-box ". This seems
a new feature, but it is merely concerted internodal growth. However, the point is
that most of the properties of the apocarpous ovary become transferred to the new
intercalation, namely the placentas with the ovules, the vascular supply, the postfertilization development of the carpel-wall and the method of dehiscence. This has
led to the quibble about the number of carpels in the syncarpous ovary, which is a
misnomer without carpels, though the functions of the original carpels have been
transferred to it in a manner suggesting the fallacious idea of fused carpels. The positions of the placentas may also be transferred within the syncarpous ovary (Puri,
1952), ending in the single terminal ovule, as in Gramineae. Then in the inferior
ovary, the original carpel-functions are variously transferred to the receptacular
tissue, or sepal-internodes, particularly the post-fertilization development of the
ovary-wall into the fruit. These well-known, but too often mis-stated, modifications of
the flower show how the transference of function puts orthodox morphology into the
state of flux in which teratological phenomena are the exaggeration. I n floral morphology, on which phylogenetic classification so much depends, it is necessary to formulate an archetype and to define both its properties and their spatial dispositions, as
Wardlaw has recommended (1956), in order to follow the diversification caused
by transference of these functions to new regions of intercalary growth. These regions,
such as the corolla-tube and receptacular tube, may be minor steps in anagenesis,
but their polyphyletic parallelism implies rather that they are also transferences
of meristematic activity from apical to basal regions of primordia ; the intercalated
regions of the flower do not add anything really new to floral construction. The
diversification, or cladogenesis, of both flower and fruit seems, therefore, to have been
largely the transference of the functions of the original free primordia to the receptacle
or parent stem, the acorn being a crowning achievement.
Fruit Examples.
As just mentioned, the properties of the syncarpous superior fruit are transferred
to the receptacular wall of the inferior fruit. Fleshy peduncles and fleshy sepals seem
to be similar examples of the transference of fruit-fleshiness, the primitiveness of which
I have argued elsewhere (Corner, 1949a, and 1953). Thus, the fleshy peduncle and
dry nut of the cashew (Anacardium)is a mango with the pulpy property of the pericarp
transferred to the fruiting peduncle : experiments with strawberries (Fragaria)
suggest that here, too, the cause may be the change in site of the receptor of the hormonic stimulus emanating from the developing embryo. I n fleshy inflorescencefruits, such as pineapple, pandan, breadfruit, and fig, complicabed transferences of
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E. J. H. CORNER:
[J.L.s.z. X L N ,
pulpy and sclerotic layers occur, recalling the transference of flower-properties in
inflorescence flowers. In the Moraceae, the original fruit seems to have been a drupe,
the fleshiness of which has generally been transferred to the sepals, as in the mulberry
(Morus),or to the inflorescence-axis as in some of the breadfruit-allies and in the figs.
The fruit of Carludovica shows transferences of the palm-fruit properties, paralleled
by Monstera in the Araceae. Similar to the Moraceae, is the case of Pernettya and
Gaultheria in the Ericaceae, Pernettya having the fleshy pericarp and thin calyx,
Gaultheria the fleshy calyx and thin pericarp ; in Vaccinium the receptacle is fleshy,
as the inferior berry. In Ricotia (Cruciferae) the pods may contain winged seeds or
the pod may be indehiscent and winged. Sterculia alata Roxb. has winged seeds and
in the allied Tarrietia it is the one-seeded pods which are similarly winged. I n the
rhubarbs (Rheum)the fruit is winged along the three angles, but in the docks (Rumex)
it is the persistent sepals, not the three-angled fruit, which may be winged. The
position of the viscin-layer in the Loranthaceae, according to Danser (1931),is either
outside the vascular bundles (Loranthoideae) or inside (Viscoideae), suggesting
transference from some ancestral position.
There are many analogies between fruit and seed in allied plants which must
express transferenceof function, and, be it noted, this transference, as withinflorescenceflowers, seems always to be from the central or apical region towards the the basal
as though the disturbing influence came from below and the centre was left solely
with the function of embryo-development. Thus, division of labour is but an aspect of
the process.
Seed examples.
It was the study of the intricate microscopic structure of the coats of large seeds
which brought this whole problem to my attention, where fortunately there had been
no theory to obscure the facts. The annonaceous seed-coat, developed from the outer
integument, has, besides layers of crossed fibres, cell-layers with crystals and celllayers with oil-cells, both of which vary in position in different genera, but the most
remarkable transference occurs in those genera with a middle, or fourth, integument
(Corner, 1949a, pp. 360-361). The middle integument develops after fertilization and
it, alone, has the characteristic fibres and crystal-cells. It seems that the normal
differentiation of the outer integument is here transferred entirely to the new integument and that there is not merely the transference from one normal structure to
another, though this, too, occurs abundantly. Thus, the palisade-layer of columnar
Malpighian cells (macrosclereids) occurs in different positions. I n several families,
of which the Leguminosae are the best example, the layer is the outer epidermis of
the outer integument (Corner, 1951). I n the Cucurbitaceae the layer is hypodermal
(Singh, 1953). I n Myristicaceae i t is the inner epidermis of the outer integument.
I n many others, as the Bombacaceae, Malvaceae, Tiliaceae, Sterculiaceae (Venkata
Rao, 1950), Euphorbiaceae (Singh, 1954), Bixaceae and Celastraceae, it is the outer
epidermis of the inner integument. The property appears to be the same in all, but
its position differs.
I extended the principle to the aril and its derivatives, arguing that the sarcotesta,
or fleshy seed-coat, which is so often associated with degenerate arils, might not be
merely the undifferentiated testa, but one to which primitive aril-properties have been
transferred (Corner, 19493, 1953). Objections have been raised by van der Pijl who
maintains the converse that the primitive properties of the sarcotesta, as found in
pteridosperms and gymnosperms, have been transferred to the aril as a new outgrowth,
similar, I suppose, to the middle integument of the Annonaceae (v.d. Pijl, 1955,
especially fig. 1, p. 59, and 1956). Our disagreement arises from the two legs of evolutionary theory, the palaeontological and the living, and I am not persuaded by
inference from pteridosperms either that angiosperms must have been derived from
them or that the sarcotesta of Magnolia is primitive or homologous with that of
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TRANSFERENCE OF FUNCTION
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Cycas. For the present my point is to show that, in order to write this great chapter
of plant-morphology on the evolution of the seed, the extreme intricacy of the structure
demands analysis into properties, sites and transfers. The aril, itself, exemplifies
the transfers because it may arise from several different parts of the seed, as from the
funicle-apex (Leguminosae,Dilleniaceae, Papaveraceae), and the micropyle also (Annonaceae, Nymphaeaceae, Myristicaceae, Bombacaceae, Celastraceae, Sapindaceae),
from the chalaza and not the funicle (Connaraceae, Meliaceae, Elaeocarpaceae),
and from the side of the seed opposite to the chalaza (Leptonychia).
Regarding strict embryology, it seems that the varying division of labour among
the cells of the early embryo, which form cotyledon, radicle and stem, results from
transference of functions in different species of a genus, or genera of a family. The
complete inversion of the embryo of Sterculia may be a reversal of polarity. Hypocotyl embryos, too, in which food is stored in the hypocotyl, must be regarded as
transferences from the cotyledonary position, or conversely, e.g. Anisophyllea,
Rarriragtonia, Bertholletia, Garcinia, Ternstroemia, and, perhaps, Rhizophora.
Shoot Examples.
Yet another ‘‘ Gestalt ”, which can be understood, is the resemblance of branchsystems to pinnate leaves. It is most striking in the Phyllantheae (Euphorbiaceae),
which seem to have simply or doubly pinnate leaves, for those on the main stems
are reduced to minute scales, and the leafy branches have limited growth (Corner,
1940, pp. 278-280). It seems that the form-factors, or properties, of the pinnate leaf
have been transferred to the axillary buds of the main stem on the degeneration of
their own leaves. But, in the Euphorbiaceae, and also in Flacourtiaceae (Casea!ria,
Hydnocarpus), where the same phenomenon occurs, no pinnate leaves are known,
though simple leaves may show pinnate lobing. I n such cases one cannot dismiss
the pinnate construction of the leaf itself, as shown in its venation, from being the
physiological basis of the phyllomorphic branch : these genes must exist in the plants
and may as well operate in the axillary buds, just as those of the flowers in Capsella
operate in the leaf-primordia.
Normally the plumule of the seedling becomes the main stem. I n many Papilionaceae the plumule has limited growth, or even degenerates in the seed, and the axillary
buds of the cotyledons take over the function of the main stem (Dormer, 1945). This
is an extreme case of sympodial growth, which is variously developed in plants so as
to cause substituting growth of the leader when it dies. Probably there is some
fairly simple hormonic control, but such cases show how variations in the site where
functions materialize affect the form of the plant. I n the epiphytic orchid Taeniophyllum there is no vegetative shoot, but a minute inflorescence, and the green
strap-shaped roots take over the physiological functions of the shoot. The mechanism
of photosynthesis is, presumably, no different from that in the leaves of other orchids,
but it has been transferred entirely to the roots. Green roots, occur, of course, in
many orchids, and comparative taxonomy will show how gradual must have been
the change over to the state in Taeniophyllum. Thus, it seems possible to explain the
well-known case of Streptocarpus (Gesneriaceae), in which a single and much enlarged
cotyledon bears the flowers and, even, the roots, in terms of transference of all functions to the cotyledon. Should we not, indeed, conclude that the secret of angiosperm
success lay in this facility of transfer P
Leaf Examples.
A simple dicotyledonous leaf has normally pinnate venation, the numerous side
veins being largest where the leaf is broadest. Some leaves, however, have the basal
.
are the trippair of side-veins prolonged, even to the leaf-apex (Text-fig. 2 ~ ) Such
linerved leaves of gentians, Caryophyllaceae, Melastomataceae, and others. The lamina
develops only in the basal part of the leaf-primordium btween the first and second
38
E. J. R. CORNER:
[J.L.s.z. XLR,
pair of side-veins, for in the tip of the expanded leaf the other side-veins may still be
found unextended. All the intercalary growth of the lamina, which makes the mesophylI between the veins, has been transferred to the interval between the first and
second pairs of side-veins, It is known that there are two processes, a t least, in leafgrowth, one making the veins and the other the filling between them, as shown by
the skeletal spring leaves of the horse-radish followed by normal summer leaves.
Phyllodic leaves, with many subparallel longitudinal veins, as in the plantains
(Plantago), are interpreted as petioles or leaf-bases extended to form a lamina, and
this is mesophyll development transferred to the intercalary growing region a t the base
of the leaf-primordium. I n Lathyrus the leaf is pinnate with distal tendrils as nonlaminate pinnae : a few species have pinnately veined leaflets, but most have phyllodic leaflets, and some have no leaflets but phyllodic petioles or foliose stipules. Thus,
TEXT-FIG.
2.-Ficus-leaves of similar shape but different venation, showing mid-ribs, costas
(main lateral veins) and main intercostal veins. I n s e t , the primary subdivision of the intercostal area by two veins NS and EW, as visible near the tips of the leaves.
A (P.annulata Bl.), parallel intercostals from NE quadrant; B (P.globosa Bl.) cascade vein from sw
quadrant ; c ( F . vasculosa Wall.) all quadrants developed ; D ( F . elastica Roxb.) sw and
SE quadrants predominant ; E ( F . indica L.) as B, but triplinerved.
in one genus, there can be traced the transfer of lamina-formation from the normal
position to the leaf-base, whence it may descend to the internode and give the winged
stem and cladode. That is why I regard such leafless, leaf-stemmed plants as cacti
as plants, not so much with dislocated chromosomes, but with dislocated sites for
gene-activity .
A more subtle process concerns the details of venation. I n Ficus, and many other
plants, the mesophyll may develop in different ways between the side-veins. At
first, a sort of square develops between a pair of side-veins, to be divided by secondary
veins into four quasi-squares (Text-fig. 2, inset). Generally the distal square (WE)
develops most to form many cross-veins (Text-fig. 2 ~ )the
, other three remainirfg little
J.L.S.B.
LVI]
TRANSFERENCE O F FUNCTION
39
changed. I n F . elastica Roxb., the two squares (SE and sw) next the mid-rib develop
to form the lamina (Text-fig.2 D ) . In P.indica L., it is the proximal square (SW) which
develops most to form a sort of cascade-vein into the axil of the lower side-vein
(Text-fig. 2 B E ) . And in other species, all the squares develop evenly (Text-fig. 2 ~ )
I n Lactuca, Camellia, Diospyros, and others the mesophyll develops largely outside
the inarchings of the main side-veins to give several series of loops. Whatever the
primitive venation of the dicotyledon, it is varied by transference of mesophyll
development t o certain parts to give the characteristic adult venation so hard to
describe until explained, and this explanation is often to be found on tracing the manner
in which the venation simplifies, or closes up, towards the apex of the adult leaf
(Text-fig. 2).
Lastly, I would recall the pitcher leaf of Nepenthes, which exhibits a basipetally
developed, or reverse, explanation of leaf-properties. It has a phyllodic, photosynthetic, winged petiole, the wings decurrent on the stem ; a n intermediate, thigmotropic, tendril-stalk without lamina ; a secretory and absorptive, basipetally
developed, pitcher as the lamina-base (so often glandular in other plants) ; and,
apically, the rest of the reduced lamina as the convenient lid, which is the first part to
be developed. Instead of being combined into one unit, as in Clematis, the leafproperties are here displayed. The experimental challenge is their recombination
into the pre-Nepenthes leaf.
Examples from Classes other than Angiosperms.
I have taken examples from flowering plants, but the principle extends to other
classes. It must enter the morphology of gymnosperm cones and embryos, the disposition of fern-sori and annuli, peristome variations in mosses, hymenial configuration
in basidiomycetes, spore-forms in rusts, and sporangial disposition, meristematic
variation, and, even, life-cycle differences in algae, such as the difference between the
generations in Cutleria, Laminaria and Dictyota. But, in the algae, we encounter
the principle of division of labour. If reproductive cells are set apart from vegetative,
the underlying process of this division of labour must be the transfer of reproduction
to those cells which evoke the reproductive metabolism. On the other hand, if the
lower cell of a two-celled embryo forms the attachment, external, not internal, stimuli
may be the cause. As Church has shown ( 1 9 2 0 ) , the organization of algae is so intimately connected with the external environment that it may not be possible to
decide by inspection whether a property is facultative and disperse, that is
materializable in many parts of the soma, or genetically localized. That the large
sporophyte of Laminaria may be reduced to a few cells in artificial culture is a
warning against speculation. I n contrast, the emancipation of the higher plant has
depended as with the animal on the evolution of the internal environment.
Jeoten y.
A function is transferred by moving the site in which the inherited property
materializes. The mutation, if any, affects the conditions for materialization. The
change may allow the property to develop earlier than usual, when it may affect a
wider, smaller, or different region of the body. Thus homaeosis, or “ t h e earlier
incidence of a morphogenetic process ” (Goldschmidt, 1938), may arise, and, also,
neoteny or the precocious maturity of an organ or organism so that it functions in
an otherwise undeveloped state. It is likely that transferences of function occur a t
developmental stages different from the original, so that both neoteny and “ gerontoteny ” are but aspects of the one principle. The importance of neoteny is widely
acknowledged. I had occasion to refer to it as “ juvenescence ” when considering
the evolution of the fruit-body in discomycetes (Corner, 1930). It seems to be the
process which has separated pollination from seed-shedding and given the precocious
flower-bud to be followed by fruit-setting, and also the smaller and simpler flower.
.
40
E. J. H. CORNER: TRANSFERENCE OF FUNCTION
[J.L.s.z.
XLN,
It is the process which has derived Lemna, as the floating aroid seedling, and the annual
herb. What is required of the systematic morphologist is the evaluation of properties,
which Church called factors of equipment, and a hypothesis of their original state and
subsequent transfer, preparatory to experimental analysis, which is often too miscellaneous for evolutionary thought. The principle of transference of function is based
upon structure, as the means for protoplasm to manifest itself by filli-ng space and
interacting with the environment, but i t operates through physico-chemical processes.
It transcends the particular disciplines of biology, and, if the capable botanist or
zoologist be now the superman, it will require a team of collaborators €or elucidation,
but the key is with the taxonomist.
Summary.
It is considered that many evolutionary changes in plants, including the division
of labour and neoteny, result from restricting the site of development of a hereditary
property or by moving it to another part of the plant-body. This principle of transference of function is explained by examples from the flower (especially Saraca)
fruit, seed, leaf, and venation (Picus) of angiosperms. Systematic morphology
should seek to define the original properties, their sites and their transfers.
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