48 West & West. — Observations on the Conjugatae. 
Other minor observations have also been brought forward 
as a proof of this sexuality, such as the comparative lengths 
of the cells and the relative thickness of the male and female 
conjugating-tubes. These are, however, of little value, although 
it is certainly a fact that in the majority of instances the female 
conjugating-tube is shorter and thicker than the male (Figs. 66, 
67, 79-81); also the female cells are often so swollen that all 
trace of a conjugating-tube is lost 1 (Figs. 67 and 81). 
In a gathering of Spirogyra velata from a stream at Baildon, 
W. Yorks., several zygospores were noticed which did not 
assume a thick wall, but germinated immediately after their 
formation (Figs. 84 and 85). 
The formation of spores without conjugation takes place not 
uncommonly in the Zygnemeae ; these asexually-produced 
spores are called aplanospores, and are produced from the 
contents of a single cell. We have noticed them in Zygnema 
leiospermum (Fig. 83), Z . pachydermum 2 and Spirogyra varians 
(Fig. 82). They have been observed by Nordstedt 3 in Zygnema 
spoilt aneum and by Wille 4 in if. cruciatum . In all cases the 
aplanospores are somewhat smaller than the zygospores, have 
a thinner membrane, and as a rule they are spherical, no 
matter what the form of the zygospore. We may also quote 
a remark made by Petit 5 concerning Spirogyra mirabilis , in 
which species the spores are produced without conjugation. 
He writes: ‘Cette tres curieuse espece ne conjugue pas et ne 
laisse voir aucun tube copulateur ; a une certaine epoque de la 
vie de la plante, les cellules se renflent vers le milieu, 1’endo- 
chrome se partage en deux parties qui se concentrent sous 
forme de globule aux deux extremites de la cellule ; il se 
forme ainsi une differentiation entre les parties de l’endo- 
1 Petit, Spirogyra des envir. de Paris, PI. IX, f. 10 ; West, Fresh w. Alg. 
W. Ireland, Journ. Linn. Soc. Bot., Vol. xxix, T. XVIII, f. 5. 
2 West, Alg. W. Indies, Jonrn. Linn. Soc. Bot., Vol. xxx, p. 266, PL XIII, 
f. 9, 10. 
3 O. Nordstedt, De Alg. aq. dulc. et Char. Sandvic, p. 17, T. I, f. 23, 24. 
4 N. Wille, Ferskv.-alg. Nov. Semlj. Ofvers. K. Vet.-Akad. Forh., 1897, No. 5, 
p. 63, T. XIV, f. 87. 
5 Petit, 1 . c. p. 14. 
