2 45 
Life- History of Isoetes . 
what longer and more pointed, but in neither is there any 
longer any trace of a single apical-cell. At the base of the 
leaf, which is now separated from the root by an evident de- 
pression, the ligule is usually (Fig. 28, x) visible, as a short 
row of cells lying close to the base of the leaf. A vertical 
transverse section of an embryo of about the same age (Fig. 31) 
shows that the ligule is already divided by walls in two planes, 
these walls being arranged with great regularity. Hofmeister 1 
compares the divisions to those in the young gemmae of 
Marchantia , and the resemblance is quite striking. The 
ligule later divides further by both longitudinal and trans- 
verse walls until it may reach a breadth of from ten to twelve 
cells, with a length of about the same (Figs. 46, 49). 
Very soon after the ligule becomes visible, the base of the 
root, which lies close to it, begins to project in the form of 
a semicircular ridge (Fig. 30, v) that grows rapidly and forms 
a sheath enclosing the ligule, together with the base of the 
leaf. The sheath increases by the division of the marginal 
cells, from whose bases cells are cut off which divide further 
and thus add to the sheath, and increase the depth of the 
space inclosed by it. A number of cells at the bottom of the 
furrow, between the sheath and the base of the leaf, constitute 
the apex of the future stem of the plant. As they differ in no 
wise from the neighbouring cells, it is quite impossible to say 
how many of them belong properly to the stem-apex. 
The Leaf . — The first leaf, as we have seen, arises from one 
of the two upper quadrants, and may for a very short time be 
said to have a single apical-cell ; but very early all trace of a 
definite apical growth is lost, and the lengthening is soon due 
to rapid division of the cells at the base. At first nearly 
cylindrical, it soon becomes slightly flattened and the primary 
tissue-systems are plainly evident. The first periclinal walls 
in the embryo probably separate the dermatogen from the 
inner tissues, which do not show a further division into ple- 
rome and periblem until a much later stage. At any rate, in 
1 Loc. cit., p, 346. 
