262 P r anker d. — On the Structure and Biology of 
well-marked endodermal sheath always surrounds the leaf-trace, which is 
often very difficult to make out in the leaf bundle. 
The roots are usually pentarch with a pith, and show a cortex composed 
of very regularly arranged cells with small quadrangular intercellular spaces, 
and a well-marked exodermis. They very often take their rise from points 
just above the leaf-gaps (Text-fig. 4), and the endodermis is always directly 
connected with that of the main stele (Text-figs. 3 and 4). Numerous roots 
are given off from branch and sometimes leaf traces in all directions, even 
as many as three from a single trace. In the case of those running more 
or less towards the centre of the stem, they sometimes encounter vascular 
tissue, in which case their direction is altered, and they find their way to 
the exterior by other routes. Instead of making their way straight to the 
exterior, the roots frequently bend and run through the cortex, or even the 
pith, parallel with the length of the stem either towards or away from the 
apex, and many are thus met in transverse section in a similar section of the 
stem (Text-fig. 5), recalling Lycopodium pithy oides, as described by Stokey 
(11), who mentions other plants in which this phenomenon occurs. 
As mjght be expected from its habit, Hottonia is markedly sensitive 
to gravity, and an examination of the character and distribution of the 
starch shows a remarkable development of ‘ statoplasts ’ ( 4 ) whose appear- 
ance coincides with the first indication of graviperception, and which occur 
at those points where curvatures take place (Figs. 13, 14, and 15). So far 
as I know, mechanism for the perception of gravity has not been described 
for aquatics, but preliminary observations seem to indicate that certain of 
them are favourable objects for the study, which it is hoped may be con- 
tinued in the near future. 
III. The Seedling. 
An unsuccessful search has been made for seedlings growing in nature, 
which are probably rare, as they do not seem ever to have been found, and 
we know that the plant has several means of vegetative reproduction. The 
following account is based on the examination of autumn seedlings obtained 
from seeds ripened on plants grown in the laboratory. These, in the case 
of both species, were extremely minute and fragile, the vascular system being 
very reduced, so that its interpretation is a matter of some difficulty. A 
seedling grown under water forms a bubble of gas between the cotyledons, 
which causes it to float to the surface, where it remains for some time, 
subsequently sinks, and takes root in the soil. Fig. 16, PI. XXI, shows three 
seedlings in which the tips of the cotyledons are still embedded in the seed 
coat, and where t marks the transition from the hypocotyl to the root, 
indicated by the cessation of the green colour and the appearance of a 
ring of root-hairs — a lateral rootlet being frequently given off just above 
