West & West . — Observations on the Conjugatae . 41 
characters of the chromatophores are not only remarkably 
constant but also widely different in many of the common 
species of the genus ; those species with toothed edges to 
the chromatophores are however the most frequent. 
The presence of straight chromatophores in the genus 
Sirogonium is in itself of no generic value, as those of Spiro- 
gyra majuscula are quite as straight, if not straighter, but 
the method of conjugation seems to us quite distinctive. 
Owing to the somewhat irregular thickening of the walls 
of some species of Zygnema , such as Z. ericetorum and 
Z. pachydermum y and the more or less non-stellate condition 
of their chromatophores, they can be readily mistaken in 
the sterile condition for species of Rhizoclonium (a genus of 
Confervaceae Isogamae), and the short, few-celled branches 
of Z. pachydermum 1 render it still more liable to an error 
of this nature. 
There are two modes of conjugation, scalariform and 
lateral , the details of which have been minutely followed out. 
In the former the cells of two or more filaments take 
part in the formation of the zygospores, but in the latter, 
conjugation takes place between the adjoining cells 2 of one 
filament only. 
If conjugation is affecting only a portion of a filament, 
the increased activity along its whole length (as previously 
mentioned) often causes the cells of its free portions to de- 
velope conjugating-tubes, which, after making futile attempts 
to meet with a fellow, become more or less irregularly 
branched 3 ; such is also the case in many examples in which 
conjugation has been interrupted. 
On examining a large number of conjugated examples of 
Spirogyra or Zygnema , there is one prominent feature which 
at once strikes the observer, and on this point we cannot 
1 West, Algae from the West Indies, Journ. Linn. Soc. Bot. Vol. xxx, PI. XIII, 
Figs. 12-15. 
2 In Cooke’s Brit. Freshw. Alg., PI. XXXI, f. 3 c, an example of lateral conju- 
gation is shown between two non-adjacent cells. 
3 Cf. West, Sulla Conj. delle Zygn., Notarisia, 1891, Vol. vi, t. 12, Figs. 3, 
5-7, and 9. 
