162 CopeLaNnpD: THE CONJUGATION OF SPIROGYRA CRASSA 
starting to form conjugating tubes with it; but the two of like sex 
never stimulated each other even enough to make the tubes start 
to grow. The filaments are then completely dioecious, and their 
sex must be determined in the zygospore. Complete dioecism is 
a higher degree of sexuality than would be anticipated in plants 
whose gametes are not visibly different* except in their part in 
conjugation. 
In much higher plants, likewise dioecious, the sex is not al- 
ways as fixed as it seems here: thus Lesquereux and James ¢ say of 
Atrichum undulatum Beauv.: “ This species is dioecious, but some- 
times the young male plant produces from the center of the flower 
an innovation bearing female flowers and thus the male plant is 
transformed into a fertile one.”’ 
In the cells of the vegetative filaments the nuclei were large 
and centrally placed, the entire contents of the cells reasonably 
clear, and no unusual bodies to be seen in the chloroplasts. In 
cells which had progressed in conjugation to the meeting of the 
‘tubes there were usually some black granules in the chlorophyll 
bands, the body of the cell remaining as clear as ever. Where 
two filaments of one sex conjugated with one of the other, or 
where one filament of a pair had shorter cells than the other, 
there were cells which tried to conjugate but failed : some of these 
merely started to put out a conjugating tube, at other times this 
stimulated the development of a tube to meet it. In all of these 
cells the contents was discolored by the presence of distinct gran- 
ules and of a diffused opacity. The shade varied from pale brown 
to deep black. The failure to conjugate has interfered in some 
way with the normal metabolism of the cells. Very likely it 1s 
that plastic matter intended for use in conjugation has accumulated 
as oil and has been blackened by the osmic acid. But it occurs 
in cells whose conjugating tube has completely formed. The pe? 
drawing is made from a cell which failed to conjugate, and is drawn 
a little lighter in shade than is natural. 
The position of the nucleus in conjugating cells was remark- 
able. A large part of my material was fixed at about the stage in 
a of his material—@ 
hape of the cells, 
* Kny (Wandtafeln, Text, 11) says that the sex of filaments 
large, not certainly identified species—was distinguishable by the s 
before conjugation began. 
+ Mosses of North America, 256. 
