304 
Smith. — A Note on Conjugation in Zygnema . 
Summary. 
Zygnema stellinum shows scalariform conjugation, with the zygospore 
lodged in one or other of the conjugating cells. 
The vegetative cell contains two complex chloroplasts, consisting of 
much-dissected fronds, incurved over a central pyrenoid. The nucleus is 
suspended in a strand of denser cytoplasm in the centre of the cell. 
The young zygospore is spherical, with a thin wall and four chloro- 
plasts. The fusion nucleus is in the centre of the spore, and is twice the 
size of the vegetative nucleus and often constricted. 
Occasional azygospores are found, which are more ovoid and have only 
two chloroplasts. 
The mature zygospore shows sculpturing of the mesosporium, which 
is yellow-brown and cuticularized. The four chloroplasts remain distinct 
even at this stage. 
In conclusion, I wish to express my thanks to Professor R. R. Gates, 
at whose instigation the work was undertaken, for his constant advice and 
criticism during the course of the investigation ; also to Mr. Gepp, of the 
Natural History Museum, for his kind assistance in identifying the 
species. 
References. 
1. Cunningham, B. ( 1917 ): Sexuality in Spirogyra. Bot. Gaz., lxiii. 486. 
2. Trondle, A. ( 1911 ): Reduktionsteilung in den Zygoten von Spirogyra . Zeits. f. Botanik, 
iii. 593. 
EXPLANATION OF PLATE XII. 
Fig. 1. Vegetative cell of Zygnema cruciatum , showing two complex chloroplasts, each with 
one pyrenoid, nucleus suspended in centre of cell in a strand of denser cytoplasm. 
Fig. 2. Young zygospore of Z. stellinum , showing four chloroplasts, less dissected than those 
of the vegetative cell. (Both figures x 2,300.) 
