Cytology of a new variety of A chlya americana. 1 7 1 
and Saprolegnia.. In other Thallophytes, however, possibly 
in the Conjugatae ( Spirogyra , Closterium , Cosmarium ), no 
reducing-divisions take place in the formation of the gametes, 
but such, it is suggested, may take place during the germina- 
tion of the zygote. In that case the Conjugatae would take 
rank, in this respect , with the higher plants. 
In animals accordingly we have always one kind of gamete, 
provided with reduced nuclei. \n plants we appear to have two 
kinds of gamete — one with reduced nuclei, in certain Thallo- 
phytes, and one with unreduced nuclei in a few Thallophytes 
and all the higher plants. Such being the case, it must be 
obvious that a reducing-division is not a necessary pre- 
liminary to fertilization. That which distinguishes a gamete 
from a spore is not the number of its chromosomes, whatever 
else it may be. 
We are in all probability a long way from the final decision 
of the nature of the differences between gametes which will 
not germinate at all and soon perish ; spores which germinate 
freely ; and apogamous gametes which germinate readily, even 
after undergoing those divisions which are normally pre- 
liminary to fertilization, as, e. g. the normally apogamous 
oospores of Saprolegnia Thureti and the artificially produced 
apogamous oospores of Achlya americana var. cambrica. 
The differences, such as they are, remain to be discovered. 
In the Thallophytes apogamy is by no means an infrequent 
phenomenon, and it may well be due to the imperfect special- 
ization reached by the gametes in these low forms. 
Strasburger’s chief difficulty in view of these complicated 
facts is to account for the occurrence of reducing-divisions 
at different stages in the course of development. He appears 
to assume that these reducing-divisions must be homologous, 
although by doing so he places all plants in contrast with 
all animals. As he is unable to conceive of a sudden 
development, such as the halving of the number of chromo- 
somes in the reproductive cells of a potential gametophyte 
during the evolution of sex (or conjugation), he takes refuge, 
illogically, it seems to me, in the sudden evolution of some 
