SECTIONAL TRANSACTIONS.—K. 383 
tubers in association with the buds. Proliferation takes place in the parent 
tuber from the cells beneath the periderm (which in places is ruptured) and 
the lenticels of the daughter tubers also proliferate. 
’ 
Friday, September 7. 
Dr. KATHLEEN BLACKBURN and Mr. J. WILKINSON.—A preliminary report 
on a cytological method of distinguishing Salix alba var. ceerulea from 
closely related species, varieties and hybrids (10.0). 
Since great difficulty has been found on ordinary morphological grounds 
in distinguishing the true cricket-bat willow (Salix alba var. caerulea) from 
spurious forms, chiefly hybrids between Salix alba and S. fragilis, the 
possibility of using the chromosome characters is being explored. ‘The 
root tip cells of Salix alba, S. fragilis, and crosses between these species, 
all show seventy-six chromosomes. These are all very small, but certain 
characteristic pairs found in SS. alba, including the bat willows, are absent in 
S. fragilis. In undoubted hybrids the characteristic chromosomes occur 
singly. Other small differences help in distinguishing S. alba from 
S. fragilis. "Typical S. alba differs from S. alba var. cerulea in having four 
instead of two chromosomes with satellites ; this is an uncertain character, 
since it is always possible for a satellite to be present but not visible. Since 
the major difficulty in the field seems to lie in distinguishing the alba- 
fragilis hybrids from the true bat willow, it is fortunate that it is just here 
that the chromosome studies afford most help. 
Dr. J. K. SpeaRING.—Cell structure of the Blue-Green Alge (10.20). 
The present investigation of the structure of the Cyanophycean cell 
emphasises the homology of the so-called ‘ central body ’ with the nucleus 
of higher plants. ‘This conclusion is based upon its structure, its behaviour 
during cell-division, and upon micro-chemical work. In Oscillatoria tenuis 
proper chromosomes are formed and apparently divide normally, although 
the appearances produced are unusual. In other related species nuclear 
division is essentially similar. In no case has a nuclear membrane been 
observed ; but in Stigonema mamillosum one or more nucleolus-like bodies 
are found in each cell of the older parts of the thallus. In some species 
the nucleus never reaches a resting stage during periods of active growth— 
the chromosomes persisting throughout the interphase. In other cases 
a well-marked reticulum characterises this stage. ‘The small size of the 
nuclei, the absence of a nuclear membrane and the presence of other sub- 
stances which stain like chromatin have been responsible for much of the 
confusion concerning the cytology of these plants. 
Dr. J. CALDWELL.— Some aspects of virus diseases in plants (10.40). 
A large number of experiments have been carried out with what have 
been shown to be two strains of the same virus, viz. the ‘ green’ and 
* yellow ’ strains of the virus of yellow mosaic of tomato (Johnson’s Tobacco 
virus No. 6). It has been found that the ‘ green’ strain has a protective 
action on plants and induces immunity against the ‘ yellow’ strain in the 
tomato plant. This and other observations have led to the conclusion that 
the differences in symptom picture presented by virus diseased plants under 
different environmental conditions may to some extent be due to the 
existence of strains in the virus causing the disease. 
The effect of one virus on another in plants has been investigated in some 
