Osborn . — Some Observations on the Tuber of Phylloglossum . 509 
is possible that some of these single-leaved plants were formed from leaves 
detached during the 1916 growing season, especially as in many instances 
the tubers from which they arose were very small and placed near to the 
surface of the soil. When plants of Phylloglossum are turgid their leaves 
are brittle and easily broken through. Apart from animal agency, a blow 
from a falling twig' or even a wind-swept leaf of Eucalyptus might 
detach one. 
The production of adventitious tubers by leaves of Phylloglossum has 
an interest quite apart from considerations of the morphology of the plant 
producing them, namely, as an instance of regeneration. It will have been 
observed that the adventitious cell mass produced on injured leaves invari- 
ably arises at or near to the proximal end of the leaf. In this respect it 
differs from the position of the cell mass formed in regeneration from 
detached leaves of Lycopodium ramulosum described by Holloway. 1 
There the leaf shows no polarity and the adventitious structure may be 
produced from any point. However, this may result from the small size 
and apparently unspecialized nature of the leaf in question. In Phyllo - 
glossum , the consistent development of the adventitious growth at the leaf 
base agrees with Goebel’s generalization — c that the place for the formation 
of new organs in regeneration is definite and is primarily dependent upon 
the direction in which the plastic substance moves in the uninjured 
plant.’ 2 
But a further consideration arises which is obvious from a study of the 
figures, namely, that while the cell mass invariably arises near the leaf base, 
it is apparently immaterial upon which side it develops in relation to the 
soil. In most cases it is developed from the side of the leaf next the soil, 
even when this is elevated by curvatures of the leaf well above the wet 
ground. But Text-figs. 12, 24, 33, show that it may be lateral to the leaf 
as it lies on the soil, and in one case, Text-fig. 29, it is from the upper side, 
i.e. that remote from the soil. Moreover, it has been noted that, with a 
single possible exception, the adventitious growth in those leaves which 
exhibit curvature is always from the convex side. Hence it seems that it 
is not merely the stimulus of contact with the damp ground which deter- 
mines the position of adventitious growth, but a morphological factor must 
be taken into consideration as well. Unfortunately it was not thought 
necessary to mark the morphological upper surfaces when detaching the 
leaves, and, as these appear nearly cylindrical, it is difficult to recognize 
afterwards, but it is possible to arrive at some conclusion from a considera- 
tion of structure. The anatomy also serves to explain the curving of the 
leaves to which reference has already been made. 
The main features in the structure of the leaf are already well known. 
1 Holloway, J. E. (1916) : Trans. N.Z. Inst., xlix, p. 88 , Figs. 14 - 20 . 
2 Goebel, K. (1900) : p. 45 . 
