156 Lloyd Williams. —Studies in the Dictyotaceae. 
it difficult in the face of these facts to resist the conclusion that the germ- 
ling produced from the tetraspore, with its sixteen chromosomes, is a young 
male or female plant, and that the segmenting oospore with thirty-two 
chromosomes to its nucleus is a young tetraspore plant. 
There is a diffiulty which will have to be explained. In certain 
localities experience has shown that it is most difficult to find a sexual 
plant. There are extensive tracts along the coast where all the plants 
seem to be the form intricata , many of which have no reproductive cells 
of any kind, and the remainder are nearly always tetrasporic. Taonia has 
a similar reduction division to Dictyota , and from analogy one would expect 
to find alternation here. Since the year 1897, however, I have not 
succeeded in finding a single sexual plant, whereas the others are found 
without difficulty. This of course is merely negative evidence, and after 
all there may be a few individuals of the gametophyte generation even 
in these localities. Assuming that the above observation is correct, one 
has to account for two things — the failure of the tetraspores to produce 
sexual plants, and the perpetuation of the former in the absence of the 
latter. This cannot be fully discussed without going into the whole 
question of environment, which will be done in a later paper. It may, 
however, be suggested : — 
1. That the same unfavourable conditions that give rise to the intricata 
form also account for the absence of sexual plants. 
2. That one of the several modes of vegetative reproduction occasion- 
ally resorted to by the plant, including perhaps the curious abnormal 
development of the tetrasporangium-rudiment above described, may enable 
the asexual generation to perpetuate itself indefinitely. 
Some hundreds of culture experiments have been tried in order to 
test the validity of the conclusions arrived at from cytological evidence. 
Plants reared from tetraspores and others from fertilized eggs have been 
kept alive for months, but owing to their sensitiveness to external con- 
ditions it has hitherto been found impossible to get them to develop 
reproductive cells. Improved methods are being tried at present, and it is 
hoped that these will be successful. 
It may possibly be urged that the two generations in the higher 
plants are generally quite dissimilar in form and structure, whereas in this 
case they are identical in both respects. Where, however, the two genera- 
tions, as in this case, are both strictly aquatic, there seems to be no inherent 
necessity for a difference of form or of structure. 
11. The Nucleolus. 
With regard to the nucleolus, it has been seen that in the earliest stage 
in all the mitoses this body is always fibrillar or granular. It is a sugges- 
tive fact that the same appearance is resumed during the prophase stage, 
