582 
Notes. 
propagation. There would be in this case an alternation of homo- 
logous generations in the sense of Celakovsky and Bower. Here 
also we have essentially to deal only with Fungi which have dimorphic 
or polymorphic propagation, with the limitation that the external 
conditions for some of the forms of propagation are so different that, 
so far as experience yet goes, these are only developed upon separate 
host-plants. 
3. In the unicellular Diatoms there is, according to the theory of 
the cause of auxospore-formation hitherto current, an alternation 
of generations in the sense that, after a definite number of cell- 
generations derived by division, the formation of auxospores follows 
by internal necessity. But it needs still more exact investigation, for 
it is quite possible that the formation of auxospores, like the formation 
of zygotes of the Desmidiaceae, is essentially dependent upon external 
conditions. In that case there would be no definite alternation of 
generations in the Diatomeae. 
4. In a number of Thallophytes, some few Chlorophyceae, above 
all in the Florideae and Ascomycetes, a fruit arises from the fertilized 
ovum, or a body homologous with it, which produces, in a manner 
peculiar to it, non-sexual cells, the spores. This spore-bearing fruit 
may be compared with the sporogonium of the Mosses, and the 
alternation of the sexual plant with the spore-fruit may be regarded as 
an antithetic alternation. But this comparison does not extend further 
than the establishment of a certain analogy. 
In the two series of the Florideae and Ascomycetes, in contrast to 
the series of the Mosses, it appears that the fruit in the higher forms 
becomes constantly more dependent upon the mother-plant, and that 
the duty of higher differentiation of the fruit falls essentially upon the 
latter. The fruit there appears not as a special generation, but as 
a product of the mother-plant. 
What, then, remains from which to derive the alternation of genera- 
tions of the Mosses and Ferns? Only Coleochaete , which, since 
Pringsheim’s celebrated investigation, has been quoted as a connecting 
link between Algae and Archegoniatae. But it has never been proved 
that the zoospores of the germinating oospore are to be regarded as 
a characteristic product of the fruit, and, accordingly, as a form of 
propagation homologous with the Moss-spores. But, on the other 
hand, it makes no great demand on our imagination to figure to our- 
selves how, in the Coleochaete-Yike ancestors of the Mosses, this step 
