The Cytology of Zygnerna ericetorum. 203 
III. Can the Genus “Zygogonium” be upheld? 
The genus Zygogonium was founded by Kiitzing in 1843' to 
include those species of Zygnerna Agardh 1824 in which the zygospore 
was located in the conjugation-tube between the two ganretangia. 
That this distinction is of no value has been shown repeatedly in recent 
years, since there are species of Zygnerna in which the zygospore 
may occupy any position from the middle of the conjugation-canal 
to the middle of the female gametangium, all these differences in 
position being sometimes found in the same pair of conjugating 
filaments. 2 Therefore, “ Zygogonium ” as founded by Kiitzing 
cannot be upheld. 
In 1858, De Bary 3 attempted to establish the genus Zygogonium 
on an entirely different basis. He described and gave two figures of 
the conjugation of Zygogonium didymum Rabenh. ( —Z . ericetorum 
type). 4 From these examples he put forward the view that the 
conjugating cells first formed “ progametargia,” which afterwards 
fused to form a zygospore. Wille in 1909 5 upheld De Bary’s view, 
although, as previously stated in this paper, his description of the 
chromatophore was erroneous. 
Since the publication of De Bary’s figures, the conjugation of 
Zygnerna ericetorum has only once been recorded and that under 
another name. Figures of conjugating specimens were published 
by W. and G. S. West in 1894 6 under the name of Zygnerna pachy- 
dermnm. The conjugated material was collected by Mr. W. R. Elliot 
from the surface of mud in a warm stream in the crater of Grande 
Soufribre in the West Indian island of Dominica. The present 
authors have re-examined the original material of Z. pachydermum 
and find that it cannot in any way be specifically separated from Z. 
ericetorum. The structure of the chloroplast is exactly the same 
1 Kiitzing, F. T. Phycologia generalis, Leipzig, 1843. 
2 West G. S. The Algae of the Yan Yean Reservoir. Journ. Linn. Soc. 
Bot. XXXIX, 1909 ; Transeau, E. N. New species of Green Algae. Amer. 
Journ. Bot. I, 1914, p. 289. 
3 A de. Bary, “ Untersuchungen uber die Familie der Conjugaten.” 
Leipzig, 1858. 
4 Through the kindness of Dr. A. B. Rendle one of the authors has most 
carefully examined the original specimens of Zygogonium didymum Rabenh. Alg. 
exsic. No. 182. {—Z. Agavdhii Rabenh. Flor. Europ. Alg., Ill, 1868, p. 253) in 
the Herbarium of the British Museum. These specimens are identical in all 
respects with typical Zygnerna ericetorum. 
« 
6 N. Wille in Engler and Prantl, Natur. Pflanzenfam. Nachtriige zu I 
Teil, Abteilung 2, 1909. 
• W. and G. S. West in Journ. Linn. Soc., Bot., XXX, 1894. 
