172 
Rendle. — On the Vesicular 
were seen on many of the transverse walls little nodules 
staining bright red with corallin-soda and bright blue with 
Hofmann’s blue; in fact reacting exactly like the callus of 
sieve-tubes and evidently consisting of the same substance. 
As this was first noticed in a resting onion, it seemed probable 
that, like sieve-tubes, the cells were only actively functional 
during vigorous growth and closed in seasons of rest. Resting 
onions were accordingly germinated, but the callus did not 
disappear, a result to be expected, since the succulent leaves 
being merely food-reservoirs do not return to active life, but 
are gradually used up as the shoot grows out. I have since 
carefully examined a great many specimens in different stages 
from young seedlings upwards, with the following results. 
In the first green leaf of the seedling the elongated cells 
contain no callus, but their transverse septa are thin and un- 
pitted. In the green leaf of a seedling only 6 \ inches long 
little nodules of callus are present on the transverse septa, 
chiefly at the corners where they join the side walls ; this was 
found in about three-fifths of the individuals examined of 
vigorously growing seedlings in warm sunny weather at the 
beginning of June. 
Examination of the parts of an ordinary small spring-onion, 
e. g. one with two green leaves and a bulb of about half-an- 
inch maximum diameter, shows the following distribution of 
callus-formation : — 
1. Succulent base of external green leaf \ Callus frequent 
and extensive on all the transverse septa and occasionally on 
the side walls ; the cells well filled with the latex (Fig. 3). 
2. Succulent base of next internal green leaf. Nodules of 
callus found on the majority of the transverse walls, but 
less in quantity than in 1. 
3. Unelongated leaf enclosed by 1 and 2. Just green at 
the tip. No trace of callus in the cells, which are still very 
small. In a similar leaf from another similar onion there 
was a very partial callus on about half the number of trans- 
verse septa examined (Fig. 2), but the leaf enclosed within 
this and about half an inch long showed no callus at all, the 
