homologous A Iternation of Generations in Plants . 357 
tion that there is, which underlies much of the misconception 
regarding alternation, and it comes out incidentally in the 
paper above quoted that this assumption is made : after 
stating that these spores of Botrydium close the first or 
sporophore generation, while the zygote is the second limit 
between the two generations, the authors remark, ‘ Alles 
Uebrige sind Anpassungs-Erscheinungen ’ : c All other phe- 
nomena are phenomena of adaptationl Are then sexuality 
and spore-formation not phenomena of adaptation ? Are both 
the stages, like the laws of the Medes and Persians, fixed 
and unalterable for all time and in all plants ? — most certainly 
not. It is found convenient and for the present reasonable to 
assume that sexuality is a uniform process throughout such 
organisms as show it, and the result of sexuality, the zygote , 
may therefore be assumed to be homologous in different 
forms, and be taken as a fixed comparable point in their 
life-cycle. For purposes of clearness of comparison, if not on 
other grounds also, this will I think be generally conceded. 
Are we justified in assigning a similar fixed position and 
general homology to the spore ? When a comparison is made 
of the archegoniate series, the stage of spore-formation is 
found (with certain rare exceptions) to recur constantly, and 
for that particular series, on phylogenetic grounds as above 
stated, the recognition of spores as homologous is perfectly 
justified ; even there however the formation of spores is to 
be regarded as a phenomenon of adaptation fixed by heredity, 
so that it recurs as a constant period in the antithetic alter- 
nation. But the question is whether this fixed character of 
the sporal stage is also to be found constantly in the Thallo- 
phytes. Those who, like Rostafinski and Woronin 1 , draw close 
comparisons between alternation in Botrydium , and that in 
Mosses or Ferns, assume that it is : to my mind, there is 
abundant evidence, even within the Siphoneae, to show that 
it is not : the mere fact of the presence of these ‘ spores * 
in Botrydium , and their absence in the sexually higher 
1 1 . c., p. 664. The authors have pointed out in the most interesting way the 
dependence of the several stages upon external conditions. 
