54 West & West. — Observations on the Conjugatae. 
under these conditions, the physiological change (previously 
referred to) from the vegetative to the reproductive cell must 
be immediately antecedent to conjugation. 
Lateral conjugation is not unknown amongst filamentous 
Desmids. Ralfs describes 1 the conjugation of two adjacent 
cells in a filament of Sphaerozosma excavatum as taking place 
between their flat ends, and we have seen an example of this 
in Spondylosium pulchrum , var. planum , from Orono, Maine, 
U.S.A. In these instances the filament does not fragment 
before conjugation, the zygospore filling up the space 
originally occupied by the two adjacent semi-cells of the 
conjugating cells. 
Aplanospores are occasionally found in the Desmidieae ; 
Bennett 2 mentions the occurrence of some spore-like bodies 
produced without conjugation in Closterium , and they are 
figured by Wallich 3 and Turner 4 in Spondylosium nitens. 
In a gathering of Desmids from the New Forest in which 
Hyalotheca neglecta was abundant, many of the cells con- 
tained aplanospores (Cf. Figs. 23-27) ; these were produced 
by the rounding off of the cell-contents and final assumption 
of a thick cell-wall. They differ in form from the globose 
zygospores, being, elliptical, with rounded poles, and when 
mature their walls turn yellowish-brown. 
Phylogeny. 
In all probability the Zygnemaceae have arisen along two 
distinct lines from some ancestral filamentous sexual 
Conjugates. The Mesocarpeae may have been developed 
through Debarya along one of these lines, and from them 
Temnogametum probably struck off at some early stage. 
Along the other line the remainder of the existing Conjugates 
1 Ralfs, Brit. Desm., p. 67. 
2 A. W. Bennett, in Annals of Botany, Vol. vi, No. 21, April, 1892. 
3 G. C. Wallich, Desm. Low. Bengal, Ann. Mag. Nat. Hist., Ser. iii, Vol. v, 
i860, T. VII, f. 10, 11. 
4 W. B. Turner, Freshw. Alg. E. India, K. Sv. Vet.-Akad. Hand!., Bd. xxv, 
No. 5, T. XVIII, f. 7, 8. 
