SPOROPHYTE. 31 
segments. The remaining 22 to 40 pairs of pinnee come out after the 
single initial is lost. In either case their actual history is the same. 
The apical growth of the leaf, with or without a single initial, gives 
rise directly to a slightly flattened and circinately curved rod of embryonic 
cells (figs. 140, 141, 144). Each margin is occupied by a row of marginal 
cells (fig. 137). Where a pinna is to develop, about six consecutive 
marginal cells elongate to form a papilla. By sectioning and halving they 
rapidly increase in number of cells and mass of tissue. The apex of the 
papilla and its manner of growth are exactly like those of the tip of the 
leaf after the loss of the initial cell (figs. 145-147). On the sides of this 
protuberance similar outgrowths form the pinnules, and on the pinnules, 
in a similar manner, the lobes of the pinnule arise, and on these again, in 
like manner, the ultimate crenations of the leaf-margin (figs. 5, 148, 149). 
From the inner ends of the oldest sections in each part of the leaf the 
vascular tissues are derived (fig. 149). In every case also there are in- 
active marginal cells between those groups which grow out to form pinne, 
pinnules, lobes, and teeth. These sluggish cells ultimately give rise to 
the tissues along the rachis between the pinne, or along the ribs between 
the pinnules, or in the notches of the pinnules (fig. 148). In the lamina 
proper, away from any vein, the sections of the marginal cell are broad 
and shallow, extending only half the thickness of the leaf (fig. 150). Each 
of the sections is halved parallel to the surface of the leaf. The outer half 
is an epidermal cell; the inner half remains single or divides again in the 
same plane and forms parenchyma (fig. 150). The ultimate marginal 
cells constitute the margin of the mature leaf. Stomata are formed while 
the epidermal cells are still polygonal in outline, and while the leaf is un- 
folding. A curved wall cuts out the stoma mother-cell on one side of a 
young epidermal cell (figs. 152, 153). The mother-cell becomes oval and 
is divided longitudinally into the two guard-cells. 
With 20 to 25 pairs of rudimentary pinne, no stomata, no air-spaces in 
the parenchyma, and no signs of fructification, the leaves emerge from 
the soil. It would be, therefore, quite a mistake to suppose that in Denn- 
stedtia punctilobula the unfolding of the leaves ‘‘consists merely in an ex- 
pansion of the leaf with comparatively little cell division’’ (Campbell, 1895, 
p. 325; 1905, p. 333), in spite of the rapidity with which the unfolding 
takes place. One-third to one-half of the blade of the leaf must be made 
outright during thistime. Ineastern Pennsylvania and Maryland the leaves 
appear above ground in the latter half of April (Cockeysville, Maryland, 
April 21; Oxford Valley, Pennsylvania., April 29,1905). By June 4 (Loch 
Raven, Maryland, 1905) spores are nearly mature. At first the petioles, 
green in all the aerial part and clothed with white hairs, elongate and unroll. 
Then the leaf spreads out from below upward. A comparison of figs. 2 and 5 
of the mature leaf and fig. 152 of a pinnule 3 mm. long from an unrolling 
leaf will give an idea of the change that goes on. In fig. 152 the stomata 
