488 Osborn. — Some Observations on the Tuber of Phylloglossum. 
In all 1 86 plants were obtained from the 300 sq. cm. (approx.) of soil. 
The figures obtained are surprising in the close way they agree with the 
result that field observations had indicated. 
Text-fig. 4. Graph showing variation in depth of current and new tubers on 1S6 plants col- 
lected from (approx.) 300 sq. cm. soil (Oct. 1917). 
Phylloglossum Drummondii , 186 plants from 300 sq. cm. soil. 
Depth of tubers in mm. 
Current. Neiv. 
Average 
io-5' io-6 
Minimum 
1 6 
Maximum 
20 15 
Mean 
10.5 10.5 
The graphic representation of the results shown in Text-fig. 4 is 
specially interesting. The depths of the current tubers give a very irregular 
flat curve with the mode at 11-5 mm. but with secondary maxima at 8 mm. 
and 14 mm. The depths of the new tubers, on the other hand, give an 
almost symmetrical curve about the mode at 10 mm. The curve, moreover, 
is a steep one, over 80 per cent, of the individuals falling between 9 mm. 
and 12 mm. 
On the Direction of Growth by the New Tuber. 
At this stage it may be well to record an observation that bears on the 
factors determining the direction of growth by the new tuber. The new 
tuber has always been found upright in the soil, its long axis being vertical. 
This suggests that gravity is the determining factor in the direction of 
growth. In compensating for excessive depth at which the current tuber 
may have been buried, the new tuber never grows erect or even hori- 
zontally. A shallower depth is attained merely by the slight amount of 
elongation made by the new tuber stalk. The flexure made by this stalk 
is always sharply downwards. Since the point upon the stem from which 
the new tuber arises is apparently determined by morphological reasons 
(this is certainly so in the case of sterile plants), 1 it may happen that when 
1 Bower, F. O. (1886),: Phil, Trans., clxxvi, p. 669. 
