434 MR. A. W. BENNETT ON THE 
agreed more or less decisively on this point, the following may 
be given as samples:—A. Male cells ‘0762 x:028 mm.; female 
cells °127 x 0432 mm. B. Male cells ‘089 x ‘0315 mm. ; female 
cells ‘1016 x ‘0381 mm. C. Diameter ‘nearly the same, 13 male 
cells corresponding in length to 10 female cells. On a broad 
average, the female cells exceed the male in both length and 
diameter by about one fourth or one fifth*. Indeed, as regards 
length, this may be seen at a glance. When two filaments have 
conjugated for any considerable length, it is very common to see 
every cell of the female filament occupied by a zygospore, while 
in the male filament there are here and there cells which have not 
participated in the conjugation: this is illustrated in fig. 2, and is 
confirmed by Wood’s drawing of Spirogyra setiformis (l. c. pl. xv. 
fig. 36), though Hassall (7. c. p. 29) has drawn the reverse. The 
cells of the male filament which are shut out from conjugation 
usually push out protuberances on the side facing the female 
filament, which, however, they do not reach, no corresponding 
protuberance being put out to meet them; less often on the side 
away from the female filament. Very rarely does one female 
conjugate with two male cells, receiving the contents of both; 
De Bary has drawn an instance of this (J. c. pl. i. fig. 17). 
An argument which has been used against the sexuality of the 
process of conjugation is that the protuberances are put out by 
both the conjugating cells, which are therefore assumed to be 
physiologically homologous. But we find that even in flowering- 
plants some advance is made towards the act of impregnation by 
the female element, as in those cases where the embryo-sac actually 
protrudes through the mieropyle in order to meet the pollen- 
tube. We need not therefore be surprised to find the same phe- 
nomenon still more pronounced when the differentiation of the 
male and female elements is so comparatively slight. Pringsheim 
(L c.) argues against the sexuality of the process on the ground 
that zygospores are occasionally formed without the cooperation 
of two cells. But even if these are ever fertile, which is by no 
* Since reading this paper, I have met with the following :—“ Spirogyra 
setiformis, var. inequalis, new var. A peculiar variety of this species, consisting 
of two sizes of filaments, the one 125 p, the other 80 p in diameter; the two 1n 
conjugation. The smaller form has the thickness and the appearance of 
S. nitida, but must be accounted a variety of setiformis. Sometimes two 
larger filaments are in conjugation, sometimes. two smaller ones; but more fre- 
quently a larger and a smaller one are united." —F. Wo tte, in Bull. Torrey 
Botanical Club, vol. x. 1883, No. 2. 
