46 Osborn . — Some Observations on Isoetes Drummondii , A.Br. 
represents a vertical section of a stock in the plane of one lobe and groove, 
collected during the vegetative season. It is seen that the functional starch- 
packed parenchyma of the stock is roughly semicircular in section. The 
starchy tissue is limited on the outside by a narrow band of cells (one or two 
wide), the walls of which are in process of becoming thickened ; this band lies 
two or three cells below the external surface. The lobe lying on the left- 
hand side of the figure is no longer a part of the storage tissue of the stock. 
It is composed of empty parenchyma cells, which at the distal portion have 
Fig. 6, a, b , and c. Series of vertical sections of stocks at different seasons cut in plane of one 
lobe and groove. Camera lucida outlines ; with the magnifications employed, the layer of prismatic 
tissue around the main xylem mass could not be indicated, a shows stock at height of vegetative 
season. Leaf-bearing surface has megasporophy 11s and internally parts of two other leaves, then 
developing scales and leaf rudiments arching over depressed apex. Parenchyma of stock packed 
with starch ; a short distance below surface a layer of cells is becoming thickened (broken line), 
eventually this completely cuts off roots. To left one ‘cap’ of lobe, its cells depleted of starch, torn 
apart and crushed, x 4-3. b shows stock at beginning of dry season. The roots have died off, 
and starch-packed tissue of stock is bounded externally by sclerized cells. Sporophyll bases removed 
for sectioning, but outline indicated ; mucilage tissue obliquely shaded ; below this, position of thickened 
cells (not yet developed) shown by broken line. Apex and leaf rudiments protected by two scales, 
the outer only thickened. To left a ‘ cap ’ completely cut off from stock, x 6-5. c shows stock at 
opening of vegetative season, when sporophylls were being shed. New season’s leaves expanding, 
position of previous season’s sporophylls shown by mucilage (oblique shading). Amount of starch 
is greatly diminished, particularly below old sporophylls. The formation of new leaf- and root- 
bearing surfaces has ruptured peripheral sclerized cells ; the expansion of these surfaces will crush 
and distort the empty parenchyma, which will eventually be cut off as caps. Position of cap (not 
shown in preparation) indicated to left by light line. x 5-3. 
become torn apart, while at the proximal side they have become 
crushed and distorted. On its free surfaces the lobe is limited by hard 
sclerenchymatous tissue. The whole of the parenchyma composing the 
lobe is moribund and in process of isolation from the stock by the layer of 
thick-walled cells that is forming around the storage tissue. 
In Fig. 6, b , a similar section of a stock is seen at the close of the vegeta- 
tive season. The peripheral sclerenchyma is continuous except below the 
mucilage tissue of the leaf-bearing cortex, across which it extends ultimately 
as far as the scales protecting the apex. The apex is roofed over in this 
