A New Species of Debarya. 89 
itself by separate walls. In each case the true diploid spore is 
contained within a structure consisting of the gametangia, the 
conjugation canal and the cellulose deposits or walls laid down by 
the gametes. 
This species— D. cruciata, seems to exhibit a further point of 
comparison, for the behaviour of the gametes before fusion, 
corresponds to that occurring in the Staurospermum-section of 
Mougestia. 
On the other hand, as West has pointed out, 2 D. desmidioides 
to which D. cruciata is related, may be regarded as indicating how 
the Desmidiaceae have arisen from such forms, through Cylindro - 
cystis. This latter is one of the Desmids which exhibits the cruciate 
appearance of the contents in its young “ zygospore ” stages. Thus 
it seems possible that D. cruciata indicates a relation between the 
genus Debarya and the Mesocarpaceae on the one hand, and the 
Desmidiaceae on the other. 
Accordingly Debarya may be regarded as a form from which 
two lines of evolution diverge, the one leading to the Mesocarpaceae 
and the other to the Desmidiaceae. There still remains the bare 
possibility, however, that the Mesocarpaceae gave rise to such forms 
as occur in the genus Debarya, and certain of these in turn led to 
the more primitive Desmids ; in other words Debarya may represent 
a link in a somewhat retrograde line of evolution, leading from the 
Mesocarpaceae to the Desmidiaceae. 
I should like to express my thanks to Professor West for 
examining the species, and to Mr. R. P. Gregory for his help and 
suggestions. 
Botany School, Cambridge. March, 1911. 
1 Wille in Engler’s Pflanzenfam. I, 2, p. 1. 
2 L.c. (1). 
Explanation of Plate II., Illustrating Mr. S. R. Price’s 
Paper on “A New Species of Debarya." 
All figures drawn with camera lucida—magnification 1,000 diam. 
Fig. 1. Single cell of vegetative filament, showing chloroplast with five 
pyrenoids. 
Fig. 2. Longer cell than that shown in Fig. 1. Relatively short chloro¬ 
plast and seven pyrenoids. 
Fig. 3. Early stage of conjugation. Each gamete contains two con 
spicuous pyrenoids. while the ends of the gametangia are becoming filled and 
highly refractive. 
Fig. 4. Later stage shewing cruciate arrangement of the chloroplast in 
the conjugation canal. Fusion has not yet taken place, and the gametes lie 
side by side. 
Fig. 5. Nearly mature zygote. The contents have laid down the walls of 
the “spore.” The walls are brown and highly refractive. The cruciate 
arrangement can still be made out very faintly. 
