4.6 West & West. — Observations on the Conjugatae. 
cells into reproductive cells be so far modified at different 
parts of the same filaments that differentiation of sex is 
brought about? Regarding the cells in this light, each one 
may be considered as an individual plant ; and why not ? 
Each individual cell is capable of living apart from its neigh- 
bours, obtaining its own nourishment from the surrounding 
medium, and its life is in no way dependent upon the other 
cells of the filament. Moreover, if we allow that the Zygne- 
meae are comparable to the filamentous Desmidieae, we 
find that the latter readily dissociate into separate cells, which 
are not at all affected by their isolation (cf. p. 30 supra). The 
only important function of the assumption of a filamentous 
condition seems to us to be in the greater facility for conjuga- 
tion afforded by the entanglement of the gregarious filaments. 
Before considering cross-conjugation it will be as well to 
consider some examples of interrupted conjugation. A keen 
observer is continually coming across instances in which 
conjugation has by some means been brought to an abrupt 
termination before the proper formation of the zygospores has 
taken place, and in these cases the spores formed are very 
variable. It may be that something has caused a cessation 
of the activity along the whole filament, or that conjugation 
has been stopped between two cells only. Fig. 69 is an illus- 
tration of the latter, the forcible pressure of a second male 
conjugating-tube having narrowed the channel of communica- 
tion to such an extent that union of the contents of the gametes 
was rendered impossible. The former is, however, much the 
most frequent. Sometimes the spore in the germ-cell is not 
of its true form l , and occasionally two spores, one large and 
one small, are present in place of the normal one 2 (Figs. 75 
and 76). When the conjugation has by some influence been 
hastened, a zygospore is often produced from only a portion 
1 Cf. Spirogyra Groenlcmdica , Rosenvinge in Ofvers. K. Vet.-Akad. Forh., 1883, 
No. 8, t. viii, f. 1-11. 
2 West, Sulla Conj. delle Zygn., 1. c., T. XIII, Figs. 27, 28; binate spores in 
Spirogyra communis, A. Hansgirg, in Hedwigia, 1888, Hefte 9 u. 10, T. X, f. 6; 
binate spore in Spirogyra Weberi. 
