Structure & Development o/Targionia hypophylla. 113 
divisions which separate off the primary wall layer usually following 
immediately upon the first longitudinal divisions in the young 
embryo, which divisions take place at right angles so that the 
upper part of the embryo consists of a series of cruciform tiers of 
four cells each. For some time the embryo is pear-shaped, with 
the upper (capsule) end broader than the lower (foot) end, but this 
stage is of short duration and soon passes over into a longer- 
enduring dumb-bell stage in which the capsule is spherical and is 
separated from the club-shaped and bluntly pointed foot by the (at 
this stage relatively thick) neck or seta portion. During this dumb¬ 
bell phase divisions occur vigorously both in the capsule and foot, 
but especially in the internal (sporogenous) tissue of the former, 
and the foot at a relatively early stage attains practically its full 
size while the capsule continues to grow and becomes eventually 
very much larger, its diameter when nearly mature being about ten 
times that of the foot. The surface cells of the foot project as 
short papillae or haustoria, these cells and also those of the 
immediately surrounding tissue of the thallus and base of the 
calyptra staining deeply. That the growing foot exerts considerable 
pressure on the tissue in contact with it is seen from the small 
size of the cells outside of the foot, but the appearance of these 
deeply-staining small cells shows also that active divisions occur in 
this adjacent tissue, so that the smallness of the cells is not due 
merely to the pressure of the foot. The space between the foot 
and the tissue of the calyptra and thallus contains deeply-staining 
mucilage, which is also seen in much earlier stages and even 
around the egg itself when the latter becomes rounded off prior to 
fertilisation. 
The differentiation of the central tissue of the capsule into 
spore-mother-cells and elaters takes place at a relatively late stage, 
and the two kinds of cells are very irregularly arranged, not forming 
rows as in Fegatella, Monoclea, Marchantia, etc. The fertile cells 
become distinguished by continuing to grow in diameter and retaining 
their deeply stainable character, while the sterile cells mingled 
irregularly with them remain small and are less deeply stained, but 
they do not grow appreciably in length until the spore-mother-cells 
begin to round off. The spore-mother-cells are described by Deutsch 
as being spherical, as is usual in the Marchantiales, but in sections 
as well as in teased out material from developing capsules these 
cells were seen to be slightly four-lobed prior to the division of the 
nucleus (Pig. 2, G), as described by Cavers (3) and Leclerc du 
