234 
THALLOPHYTES. 
I. Conjugation and Productioji of Zygospores. Two cells of similar if not 
always of precisely the same nature coalesce, and produce a reproductive cell 
termed a Zygospore, which germinates after a shorter or longer period of rest, and 
then gives rise either to spores or at once to a plant of the same kind as that in 
which the conjugation took place. An alternation of generations is exhibited only 
in so far as the zygospore constitutes the entire second (non-sexual) generation. 
The process of the formation of zygospores has a very different appearance 
according to the nature of the conjugating cells. The simplest case is presented 
Muscinese ; for the zygospore is homologous with the spore-capsule of Mosses, 
and represents a rudimentary alternate generation. The conjugation of Spirogyra, 
as illustrated in Fig. 6, p. lo, is somewhat more complicated. The conjugating 
cells are here surrounded by a firm cell-wall ; they put out protuberances opposite 
to one another, which unite to form a canal, through which the contents of 
one cell pass over into the other, and coalesce with its contents ; the resulting 
protoplasmic body invests itself with a cell-wall, and becomes a zygospore, which 
again produces a Spirogyra filament by direct germination. The formation of 
zygospores in the Zygomycetes is represented in Fig. 162, B. Here the two cells 
which coalesce after having grown towards each other are perfectly alike and immotile ; 
and it is only a portion of the coalesced contents which becomes separated by a 
partition-wall, and produces the thick-walled zygospore which germinates after a 
period'^ of rest. 
2. The Formation of Oospores in Oogonia. The two reproductive cells are 
here essentially different; the female cell or Oosphere is always a naked immotile 
primordial cell developed within an older cell which is termed the Oogonium. 
The male cells, the Antherozoids, the mother-cells of which are called Antheridia, 
are very small, and are endowed with motion by means of vibratile cilia ; they 
swarm round the oosphere, and cause its impregnation by the coalescence of their 
Fig. 162. — Various forms of conjutfation and the production of zygospores ; 
A conjugation of the zoogonidia of Pajzdnrüia ; H formation of zygospores 
in Piptocephalis (after Pringsheim and Brefeld). The numbers indicate in 
each case the successive stages of development. 
A 
in the conjugation of zoogonidia 
discovered by Pringsheim (Fig. 
162, A). These bodies during 
the process of swarming come 
into contact in pairs by their 
hyaline anterior ends, and then 
gradually coalesce into a primor- 
dial cell, which subsequently be- 
comes invested with a cell-wall, 
and then grows, producing again 
motile cells, and each of these 
gives rise to a plant of the ori- 
ginal kind. These Zoospores which 
result from the zygospore may 
be considered as true spores in 
the same sense as those of the 
De Bary, Thuret, Nägeli, Janczewski, Brefeld, and others ; though a different signification to 
that of the authors is sometimes applied to them. 
