2 
the base of that which preceded it, while the axis was in course 
of time derived from their superposed basal portions. In this 
way, it is argued, the leaf became pushed to one side and assumed 
the lateral position which it occupies to-day ; its development 
gradually became arrested, and by lagging behind the succeeding 
internode it now appears lateral in origin. 
In the seedlings .of certain monocotyledons—for instance, 
Juncus, Sparganium, and Pistia—it has been shown that the 
first few leaves arise one from the base of the other, and that to 
begin with there is no axis visible. Very soon, however, it can 
be seen making its appearance, at first hardly discernible, but 
more and more prominent as each successive leaf is produced, 
till finally the leaves arise upon it in quite the normal way. Just 
as the zoologist has found impressed on the developing mam- 
malian embryo the shadow of its phylogeny, so do these botanists 
who believe in a terminal leaf see a proof of their theory in the 
ontogeny of such a seedling. Against this it is argued that a 
fuller investigation will probably show that the conditions 
existing in those unusual cases can be best explained as arising 
from a more or less complete arrest or even suppression of the 
axis; and since the species in which the peculiarity has been 
noted are chiefly hydrophytes and geophytes, it is suggested 
that the cecological conditions which have given rise to such 
types of vegetation may also tend to produce this sort of seedling 
structure. 
At the suggestion of Professor Bayley Balfour, I began, in 
_ the autumn of 1905, a careful investigation of the structure of 
monocotylous seedlings at various stages during and after 
germination ; and also of embryos taken from ripe seed. Since 
then the greater part of my time has been occupied by the work, 
and I have collected a large amount of material, much of which 
has now been carefully examined. The effect of deep and shallow 
seed-sowing upon the various organs of the young seedling, 
and the development of the plumular meristem, have in particular 
been kept in view, not only when germinating the seed, but also 
in the cutting and examination of sections. The object of this 
paper. is to put on record some of the results obtained, chiefly 
‘as regards the latter question. 
After some thought I have decided that the best way in which 
‘to avoid confusion is to select a small number of the plants 
examined, to describe these fully, and to give in each case a list 
of those species which, in the matter of their plumule, resemble 
the type chosen. An attempt has been made to so arrange the 
examples that they may form a series, beginning with one in 
which the leaves always appear lateral, and ending with as 
extreme a case of stem suppression—if indeed it be such—as 
