578 
Notes . 
of the Archegoniatae, any more than does that of the other Thallo- 
phytes which have been mentioned. 
But now the question arises whether there is not in many Thallo- 
phytes another form of alternation of generations, which presents nearer 
relations to the phenomena in the Archegoniatae. The fertilized ovum 
develops according to the statements of investigators in a definite way 
in certain species : thus, for instance, the zygospore of one of the 
Mucorineae, the oospore of Vaucheria and of Saprolegnia , usually 
germinate by formation of a short tube, which directly bears a 
sporangium. Pringsheim speaks, in such a case, of the first neutral 
generation : we might regard this as the actual spore-forming genera- 
tion, corresponding to the sporophyte of the Mosses. Closer investiga- 
tion shows that an oospore of Vaucheria shows no tendency in any 
way fixed by heredity to form a sporangium. It produces first a short 
germinal tube, which may either continue its vegetative growth, or may 
at once form zoospores, or sometimes sexual organs. That would 
depend alone on external conditions. De Bary and I myself have 
lately proved the same for the oospores of Saprolegnia , and Van 
Tieghem for the zygospores of the Mucorini. There is no true 
meaning in speaking of an alternation of generations in these cases, 
since the formation of the sporangia is not a peculiarity of germination, 
but follows the same conditions as it does subsequently. These plants 
do not behave differently in principle from the Fucaceae, or Conjugatae, 
in which the fertilized ovum passes more or less directly into the 
thallus, since no other propagation exists at all. 
But there are perhaps other species in which the mode of germina- 
tion of the oospores has become more definite. The zygotes of Hydro- 
didyon show, according to Pringsheim, a characteristic mode of 
germination, but it is not yet known exactly how far it is a constant 
process. In Oedogonium the germinating oospore forms four zoospores 
— a process which does not occur again in its later life. The manner 
of germination is not absolutely indispensable, since the oospore also 
passes over directly into a filament, though it appears to be the commoner 
case. Still more peculiar is the germination of Coleochaete as described 
by Pringsheim, in which the fertilized ovum divides and forms a tissue, 
from the cells of which zoospores arise, which then grow on into the 
typical thallus. There are no exact investigations whether this kind 
of germination is a constant phenomenon, since the germination has 
only been observed by Pringsheim, under conditions which were 
