West & West . — Observations on the Conjugatae . 43 
Normal conjugation depends to a certain extent on the 
general surroundings of the filaments, many hindered and 
consequently irregular examples being met with in every 
gathering in an active state of conjugation. On rare occasions 
hybrids are produced, one species of Spirogyra conjugating 
with another of different thickness ; examples of this are 
N. maxima , var. inaequalis 1 , and some smaller species gathered 
in 1893 on Mitcham Common, Surrey (Figs. 70 and 71). Several 
abortive attempts at hybridism were seen in this gathering, the 
two examples figured being the only two observed with thick- 
walled zygospores. These spores were of variable form and 
dimensions, and were present in both filaments. 
In contradiction to Cooke, we find scalariform conjugation 
to be much commoner than lateral conjugation, as may be 
gathered from the following table. 
No. of gatherings 
No. of gatherings 
of scalariform 
containing lateral 
Species. conjugation examined 
conjugation 
during the past 
examined in 
few years. 
same period. 
S. ajftnis ... 
1 
3 
S. angolensis 
... 1 
S. arcta ... 
2 
S. bellis ... 
6 
1 
S. calospora 
1 
S. cataeniformis ... 
4 
S. communis 
5 
S. condensata 
9 
S. crassa ... 
9 
1 
S. cylindrospora ... 
S. decimina 
3 
S. dubia ... 
1 
S.fusco-atra 
1 
S. gracilis , and v.Jlavescens 
••• 13 
i 
S. Grevilleana 
4 
S. injlata ... 
1 
... 2 
S. insignis 
4 
S. Jurgensii 
... 2 
... 1 
S.longata... 
... 13 
S. Lutetiana 
1 
S. majuscula {S. ortho spira) 
... 2 
S. maxima (S. orbicularis') 
1 
1 Wolle, Freshw. Alg. U. S., PI. CXXXVIII, Figs. 5 and 6, and PI. CXLII, 
Figs. 5 and 6. 
