Download xxiii the haploid nuclei of the amoebulae united to form the diploid

INTRODUCTION
xxiii
the haploid nuclei of the amoebulae united to form the diploid
nucleus of the zygote, of which these nuclei in the plasmodium
are the descendants (16, p. 244). In the genera Badhamia,
Physarum, Trichia, and Arcyria sixteen chromosomes have
been counted in the dividing nuclei of the plasmodium, and
eight in those of the swarm-cells ; while Harper counted twelve
chromosomes in the diploid nuclei of Fuligo (10).
The Sporangium.—The formation of the sporangium has
been minutely described by de Bary (2, p. 424), and a brief
notice of the' general characters will be sufficient here. In
many cases as long as the supply of food is sufficient so long
will the plasmodium continue to feed and grow ; when the
nourishment is exhausted it prepares to pass into the fruiting
stage : but in other cases sporangia develop when the food
supply appears to be still abundant, and the cause of the
change is then obscure. Preparatory to sporangia being
formed the plasmodium usually leaves the moist surroundings
where it has been feeding and creeps to some drier place more
suited to the dispersion of the spores. It concentrates at
certain points and develops into sporangia of the forms
characterstic of the species.
In examining the rising sporangia of Physarum nutans in
a moist chamber under the microscope, the projecting masses
of plasmodium are seen to pulsate, swelling or shrinking as the
rhythmic flow advances or retreats, but gradually growing with
the advancing movement. As the sporangia develop, an
envelope, the sporangium-wall, is secreted by the protoplasm
at the surface. It is at first of a gelatinous consistency, but
ultimately becomes membranous. The basal walls of the
young sporangium in this species usually form a stalk, a tube
of tougher substance, through which the protoplasm continues
to flow until the surrounding veins have emptied their contents
into the spherical head ; the walls of the stalk then contract
upon themselves and provide a firm support for the sporan­
gium. The stalks of adjacent sporangia, or the sporangia
themselves when sessile, are often connected at the base by
a membrane or membranous strands secreted by the remains
of the plasmodium ; this is termed the hypothallus. During the
formation of the sporangia all waste matter which may have
been ingested by the plasmodium is discharged, some of it
being often deposited in the cavity of the stalk or within the
hypothallus.
Soon after the formation of the sporangium-wall, a system
before Spore-formation ; assuming t h a t it occupies an equal time in the growing
Plasmodium, and t h a t during those fourteen hours the nuclei h a d increased fourfold
(an increase corresponding with the growth of the P l a s m o d i u m ) , it is difficult to see h o w
mitosis could have escaped detection if it h a d been widespread and affecting m a n y
nuclei simultaneously. T h e size of the nuclei varied from 2-5 to 5 M. a n d occasionally
there were appearances suggestive of direct division taking place, b u t these m a y p o s s i b l y
have been due to the overlapping of one nucleus on another ( 2 1 ) .