Osborn. — Some Observations on Isoetes Drummondii , A.Br . 45 
split surface of the groove, and the scar surface. This last in aquatic 
species is more or less irregular, formed by decay or removal of the distal 
ends of the lobes after the leaves and roots borne on that region of the stock 
have ceased to function. 
In Isoetes Drummondii the lobe is formed of a series of nested caps, 
representing successive season’s growth. Each cap is bounded externally 
by thick-walled brown cells, bears the remains of roots, foliage-leaves, and 
scales of a previous season upon the lower and upper surfaces, and has also 
two scar surfaces. To the outer of these the more distal cap was attached, 
Fig. 5. A single * cap 5 or desquamated stock lobe, a , the leaf-bearing surface, shows externally 
(i.e. nearer the observer) the remains of sterile leaves, some being cut away on the right, and 
internally two scale-leaves that protected the growing apex. The surface between was occupied by 
sporophylls, three scars formed by the leaf-traces of which can be seen, b, the root-bearing surface, 
with remains of one season’s crop of roots, f, the distal ‘scar’ surface, to which a similar cap 
formed the preceding season was attached, showing withered remains of root-traces of previous 
season. 
while the whole proximal scar surface of the cap is composed of dead 
parenchyma cells. In this manner the old cortex of both leaf- and root- 
bearing portions of the stock is sloughed annually, giving rise to the caps, 
but it is not removed, since the soil holds it in position. A. Braun 1 noted 
this annual desquamation of the lobes of the stock, though he had not the 
knowledge of the plant in the field to connect the phenomenon with the 
seasonal changes that occur there. 
5 Cap ’ Formation on the Lobes . 
The formation of a cap can most easily be followed in a series of 
median vertical sections of the stock taken at different seasons. Fig. 6, a , 
1 Braun, Alex. : Monatsbericht d. Iv. Akad. d. Wiss. Berlin, 1 868, p. 543. 
