Carter. — Studies on the Chloroptasts of Desmids. /. 251 
D. Summary of the Special Characters of Xanthidium. 
In those species of Xanthidium examined, two distinct types of chloro- 
plast were observed. 
A few species were found to have axile chloroplasts. These invariably 
had two chloroplasts in each semi-cell, there being typicallyone pyrenoid in 
the centre of each. 
The remaining species examined had parietal chloroplasts, and here 
there were usually four in each semi-cell. In all these species, with the 
exception of X. armatum , there was typically one pyrenoid in the centre of 
each chloroplast, but in this very large species the pyrenoids were both 
numerous and scattered. 
X. Brebissonii seems usually to have chloroplasts of the first type, but 
the pyrenoids frequently become very numerous, and the chloroplasts often 
tend to become partly parietal. 
In conclusion, I wish to express my sincerest thanks to Professor 
G. S. West for much valuable help and advice during the course of the 
work, and also for supplying much of the material. I am also deeply 
indebted to the Birmingham Natural History and Philosophical Society for 
a grant from their Endowment of Research Fund, to help in the cost of 
reproducing the plates, and also to the Royal Society for a further grant 
for the same purpose. 
The Botanical Laboratory, 
University of Birmingham. 
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