Osborn . — Some Observations on the Tuber of Phyllog lossum. 489 
the current tuber is very deeply sunken the plant cannot in one season 
adjust the new tuber to the normal or average depth. Thus two plants 
having the current tuber buried to 30 mm. produced their new tubers at 
1 5 mm. and 14 mm. respectively. Assuming no change occurred in the 
ground-level, the new tubers of the ensuing season would also be on short 
stalks ; thus two, or even three, seasons might pass before the average 
depth was established. 
An example of the influence of gravity upon the direction of growth of 
the new tuber stalk was furnished by a plant growing in the laboratory. 
In cutting a sod of soil, to be kept moist under a bell-glass for experimental 
purposes, the trowel accidentally exposed, without damaging, the new tuber 
stalk of a five-leaved sterile plant. The stalk at that date (July 31, 1918) 
was still short, the apex unswollen. It continued to grow, exposed 
to light, descending vertically through 19 mm. before it buried itself in the 
silt at the bottom of the dish (October 21, 1918). The growth here was 
clearly geotropic. Light had no influence upon it, for the stalk, though it 
developed chlorophyll throughout its whole exposed surface, made no 
phototropic response. This observation is of some importance when con- 
sidering the behaviour of tubers produced by detached leaves. 
On the Rate of Development of Fhylloglossum in 
Successive Seasons. 
The sporeling of Phylloglossum described by Thomas 1 is single leaved 
and rootless 2 in the first season of its growth. The number of leaves may 
be assumed to increase from year to year as successive seasons’ activities 
allow more starch to accumulate in the new tubers. 3 Thomas records that 
the further development of the sporophyte appears to be slow. ‘ In many 
cases the plant comes up a second and third year with only a single leaf.’ 
This he determined by carefully dissecting plants from the soil, and so 
finding the remains of former years’ tubers and roots. 4 
After a little practice it was found possible to remove the remains of 
the old tubers, together with the plant to which they belonged, without 
disturbing their relative position one to the other. Text-fig. 5 shows 
a single-leaved plant collected about a month after the first winter rains. 
The root is hardly developed and no new tuber is visible at this date, but, 
in addition to the current tuber, the decaying remains of the tubers formed 
1 Loc. cit., p. 288. 
2 Sampson, K. (1916) : Ann. Bot., xxx, p. 605. The sporeling described by Miss Sampson 
was also single leaved, but had a slender root. 
3 The number of leaves in any season, of course, is not determined until after germination of the 
tuber. Bovver, F. O. (1886) : loc. cit , p. 667. 
4 Loc. cit., p. 288. 
