SIGNIFICANCE OF THE SEXUAL PROCESS. 55 
most highly organized plants, at the close of their life-cycle, to the unicellular 
condition: in a word it is the repetition of phylogeny in ontogeny (I. c., 
p. 311). 
This theory of reduction must still be regarded as a very helpful 
working hypothesis, finding its greatest application in the higher 
plants. In the lower cryptogams the theory is confronted with facts, 
many of which seem at present to be quite at variance with it. The 
product of fecundation in the 7Zallophyta as a rule does not give rise 
toa definite organism representing the asexual generation, and it is not 
known at which point in the life-cycle that reduction takes place. It 
has been suggested that reduction may take place during the germina- 
tion of the zygote or odspore. Conclusions respecting the time of 
reduction in the lower cryptogams have been drawn chiefly from the 
phenomena of certain cell-divisions that seem to be analogous with 
divisions which follow the reduction in higher organisms, and not 
from an actual determination of the number of chromosomes. On 
account of the many difficulties in counting, the number of chromo- 
somes is known in only a very few alge and fungi, and our knowledge 
on this subject is so meager with respect to these plants that the few 
definite facts that have been obtained, although apparently at variance 
with the theory, may not as yet be considered as offering very serious 
objections to it. 
If the reduction in the number of chromosomes signifies what is 
attributed to it by the theory, it is possible, in the light of facts that 
have been observed in such algz as Fucus and Dictyota, that what is 
considered the sexual generation in the Thallophyta may not be 
homologous with the gametophyte of higher plants, assuming that 
homology is based upon the number of chromosomes. Farmer and 
Williams (’96, ’98), and Strasburger (’97) have found that the reduced 
number of chromosomes in Facus appears in the odgonium, while in 
vegetative cells of the thallus twice that number is present. Stras- 
burger finds that in the first nuclear division in the odgonium the 
reduced number appears, fourteen to sixteen having been counted, 
and this number persists throughout the two succeeding mitoses. In 
vegetative cells of the thallus, which is regarded as the gametophyte, 
the number is not far from thirty. In Dzctyota 1 have found the 
reduced number (sixteen) of chromosomes in the first nuclear division 
of the tetraspore mother-cell, while in the vegetative cells of the thallus 
bearing the tetrasporangia about twice that number was counted. 
Whether in the nuclei of plants arising from tetraspores the reduced 
