44 West & West . — Observations on the Conjugatae . 
No. of gatherings 
No. of gatherings 
of scalariform 
containing lateral 
Species. 
conjugation examined 
conjugation 
during the past 
examined in 
few years. 
same period. 
S. negleda v. ternata 
1 
1 
S. nitida ... 
... 17 
S. porticalis 
3 
S. setiformis 
S. Spreeiana 
2 
S. tenuissima 
... 
16 
S. varians ... • 
6 
4 
S. velata ... 
1 
S. Weberi 
7 
1 
S. Welwitschii ... 
1 
Total 
... 123 
3 2 
Lateral conjugation is 
much rarer in 
Zygnema than in 
Spirogyra , and although 
it is figured in 
various works ; we 
have never yet seen an 
example of it. 
It is figured by 
Schmidle 1 in this genus in 
a species which he names Zygnema 
(Zygogoniuni) Heydrichii , but of which he gives no proper 
diagnosis 2 . 
Scalariform conjugation being far more predominant, we 
may say that lateral conjugation is the exception rather than 
the rule, and in view of this we may regard it with some 
amount of truth, as brought about by conditions unfavourable 
to conjugation in the natural or scalariform way. It may 
be thus considered to a certain extent as abnormal, and to 
what extent this abnormality is carried may be gathered 
from a consideration of Fig. 68 (drawn from an example from 
Mitcham Common, Surrey), in which specimen conjugation 
has taken place through the ends of the cells, and the con- 
jugating cells have become genuflexed near their junction. 
1 W. Schmidle, Zur Entwickelung einer Zygnema und Calothrix, Flora, 1897, 
Bd. 84, Heft 2. 
2 This species seems to us to be only a Zygnema spontaneum with lateral conju- 
gation. Nordstedt only found aplanospores when he described the species, but we 
have since found the zygospores (cf. Figs. 60 and 61) produced by scalariform 
conjugation (Journ. Bot., Feb. 1897, p. 40). The zygospores seen by Schmidle 
and produced by lateral conjugation agree in every way with those we saw in 
Zygnema spontaneum \ moreover, the plants are of the same dimensions. 
