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S. Reginald Price. 
pyrenoids, of which two or three are usually larger and more 
conspicuous than the rest. 
The process of conjugation is very similar to that described 
for D. desmidioid.es, West 1 and D. Hardyi, West. 2 
The horns of the young “zygote” become filled by a deposit 
of cellulose as the gametes recede while at the same time the ends 
of the semi-gametangia round off. As the zygospore ripens these 
semi-gametangia apparently decrease in length, probably through 
the expansion of the conjugation canal. 
The behaviour of the gametes can be followed for some time. 
As they recede into the conjugation-canal some of the pyrenoids 
decrease in size and become less distinct finally disappearing 
altogether, while two in each gamete enlarge and become more 
conspicuous. The gametes pass into the canal, as V-shaped masses 
with their apices directed towards one another. They may be seen 
lying side by side in the canal, the line of apposition being the short 
axis of the zygote. At later stages the two pyrenoids in each 
become still more distinct, and probably by this time all the others 
have disappeared ; the fusing gametes therefore give the appearance 
of a four-armed cross, each segment of the cross containing one 
conspicuous pyrenoid. The walls of the “ spore ” now proceed to 
thicken considerably and become golden brown and highly refractive. 
The pyrenoids diminish in size and become indistinct; the cruciate 
arrangement of the contents persists, however, till a late stage, but 
finally disappears. The behaviour of the nuclei has not been 
followed, but it may be presumed that fertilisation takes place at 
about this stage. 
A similar cruciate arrangement in the young “ zygotes,” is 
met with in those species of Mougeotia belonging to the section 
Staurospermuni and in the Desmids Cylindrocystis and Penium 
didymocarpum. 
In such species of Debnrya as D. Hardyi, D. desmidioides and 
the one under consideration, it seems hardly correct to regard the 
whole contents of the gametangia as entering the zygospore 1 for 
the gametes as they recede deposit the cellulose thickenings of the 
semi-gametangia. The whole “ zygospore ” structure in the case of 
Debarya may, perhaps, be homologised with the so-called sporocarp 
of the Mesocarpaceae. In each case cellulose is laid down by the 
gametes, probably before fusion of the nuclei has taken place, and 
the product of this final fusion-the true zygospore—surrounds 
1 L.c. 
2 West, G. S. Journ. Linn. Soc. Bot., 1907, XXXVIII, p. 104. 
