A Note on Conjugation in Zygnema. 
BY 
EDITH PHILIP SMITH. 
( From the Department of Botany , King's College , University of London , ) 
With Plate XII and two Figures in the Text. 
ATERIAL. Certain preserved material of Zygnema , which was 
1 KZ known to have been in the possession of the Department for 
a number of years, although it was unfortunately impossible to discover 
its source, was found on examination to show abundance of zygospores. 
As conjugation in Zygnema is rare in nature, and has not hitherto been 
induced experimentally, it was felt that a preliminary account of the stages 
shown in this material would be of interest. In order to confirm the 
observations on the structure of the chloroplast in the fixed material, fresh 
material of another species (showing only the vegetative stage) was also 
studied. The resemblance in general character of the chloroplasts in the 
two species was very striking. 
Treatment. The preserved material was in 70 per cent, alcohol, but 
as an additional precaution was fixed for 24 hours in dilute chromacetic 
acid. It was then placed in 5 per cent glycerine, which was concentrated 
until of the thickness of pure glycerine. The material was then stained in 
safranin and aniline blue, and mounted in Venetian turpentine. Material 
thus treated showed the nucleus stained pink, the chloroplasts light blue, 
while the pyrenoid took a very dark blue. The cytoplasm remained 
practically colourless. Paraffin sections 6 /x thick were also cut, and stained 
with Heidenhain’s iron-alum haematoxylin, but owing to the small size of 
the nucleus and the originally imperfect fixation, no details of nuclear 
structure were made out. 
The fresh material was studied in #ater and iodine mounts : the latter 
reagent brought out very clearly the structure of the chloroplast and the 
pyrenoid. 
Description . By comparison with herbarium material at the Natural 
History Museum, the conjugating material was identified as Zygnema 
stellinum , (Vauch.) A g. The fresh material corresponded to Z. cruciatum. 
[Annals of Botany, Vol. XXXVI. No. CXLIII. July, 1922 ] 
