248 
William J. Hodgetts. 
relation then does this alga stand to “ Zyguenia pachydermum ” 
W. & G. S. West, which, according to West and Starkey (9, 10,) is 
identical with Zygog. cricetorum ? It may well he that the latter 
authors are correct, while the process of conjugation described 
for “Z. pachydermum ” may be abnormal, and a result of the 
peculiar conditions under which the alga was found growing in 
the W. Indies. The high temperature of its habitat (a warm 
stream in the crater of a volcano) may have supplied the extra 
stimulus which induced the alga to conjugate in a more direct 
way, after the manner of certain species of Zygnema. Indeed, 
may not the condition found in •“ Z. pachydermum" be a reversion 
to the method of conjugation employed by the immediate ancestors 
of Z. ericetorum P 1 The peculiar method of conjugation, which 
must now be considered as normal in the latter species, was 
possibly derived from the ordinary Zygnema- method, by the fusion 
of the gametes being greatly delayed—a result of the lethargic 
and *• inert ” character of the alga—and a consequent need for 
extra protection of the gametes ; the various new stages thus being 
looked upon as intercalated into what was originally a method 
similar to that found in the species of Zynema in which the 
zygospore is lodged in the conjugation-canal. 
In its cytological characters (9, 10, 4) Zygogonium ericetorum 
obviously stands in close relation to Zygnema and Pyxispora, and the 
three genera are best placed together as a sub-family of the family 
Zygnetnaceae—following the modern tendency to utilize chloro- 
plast-characters as the basis of the subdivision of this family. It 
is interesting to note that, in the fact that the gametes are cut off 
in special gametangia, Zygogonium ericetorum stands in exactly the 
same relation to Zygnema, as Sirogonium does to Spirogyra, and as 
Temuogametum does to Mougeotia. To make the type of conjuga¬ 
tion observed in Zygogonium the basis of a special sub-family in the 
Zygnetnaceae—as, for instance, is done by Wille (13)—seems very 
undesirable, as it quite obscures the obvious relationship of the 
genus to Zygnema. 
The formation of the gamete from only part of the protoplast 
is a character which many algologists consider of great importance, 
Wille (13), for instance, uses it as the basis of his Mesocarpaceae— 
a family which should thus logically include Zygogonium ericetorum 
and Pyxispora, as well as Mougeotia and its allies. If, however, 
1 Nevertheless the possibility of “ Z. pachydermum" being a species 
distinct from Zygog. ericetorum— although showing identical vegetative 
characters—must be borne in mind. 
