Osborn.— Some Observations on the Tnber of Phy l l og l os sum. 487 
stalk, hence it may be buried in the soil two or three times its own length 
deeper than the current tuber. 1 
The examination of any considerable number of plants collected at one 
time from the same locality shows that the depth at which the new tuber 
is formed in the soil in relation to ground-level is not a matter of chance, 
but is the result of definite growth of the plant producing it. If, for any 
reason, the current tuber is buried by deposition of more soil above it, the 
burial is compensated for by the development of a short stalk bearing the 
new tuber. Conversely, if, by removal of surface soil, the current tuber is 
brought near to the surface, the new tuber is sunken to a greater depth. 
There are two sets of climatic conditions that tend to produce an 
alteration of the ground-level in the area where Phylloglossum has been 
studied near Adelaide. 2 In the wet season (April to October) or during 
periods of heavy precipitation, which occasionally occur in the summer, 
there is, owing to local irregularities in the ground, a flow of water over the 
surface in many places. This causes a removal of soil from some areas and 
its consequent deposition over others. Since the ground over the greater 
part of the area is almost flat, the amount of change in level is slight ; but 
very slight changes have a considerable effect on such a minute plant. 
On the other hand, during the dry season, when for weeks together the 
surface layers of the soil are desiccated, atmospheric denudation causes 
similar slight changes in ground-level. Such variations may not exceed 
a few millimetres rise or fall, but they influence to a marked degree a plant 
whose total length from tip of leaf to base of tuber may be less than 3 cm. 
and the optimum depth for whose tuber lies between 10 and 12 mm. 
On the Depth of Tuber Formation — Statistical. 
In order to gain a clear idea of the depths at which the tubers of 
a number of Phylloglossum plants taken from any area may occur, three 
typical groups of plants were selected in October (i. e. near the close of the 
growing season) and a sod of soil some 10 cm. square cut from each. The 
three sods were carefully removed to the laboratory, where every plant was 
dissected out. Two measurements were then made upon each plant, viz. 
the maximum depths of the current and new tubers. The points of 
measurement selected were the ground-level (usually sharply defined by the 
development of chlorophyll) and the deepest point of the tuber. It was 
found desirable to include the length of the tuber in the measurement in 
order to avoid minus quantities when the tuber was partly exposed, and also 
because the distal end of the tuber is well defined while the proximal end 
passes gradually into the stalk. 
1 Bertrand’s figure of Phylloglossum reproduced in Campbell, D. H., Mosses and Ferns, 
p. 501, Fig. 290 A, shows this condition, but to a less extreme degree than either of the plants figured 
above. I regret I have not been able to consult a copy of Bertrand’s memoir in Australia. 
2 Osborn, T. G. B. ( 1918 ) : Trans. Roy. Soc., S. Aus., xlii, p. 7. 
N n 2 
