4 § Osborn. — Some Observations on Isoetes Drummondii , A.Br. 
invaginated growing apex and the negligible growth in length of the stem 
each year, forces the exhausted parenchyma outwards, laterally, and so leads 
in Isoetes Drummondii to the development of three lob£s corresponding to, 
and alternating with, the three lines of growth in the root-bearing region. 
Roots. 
The roots of Isoetes Drummondii function only for the few months of 
each growing season, and then die off. Every year a completely new root 
system is produced on a new root-bearing surface 
of the stock (Fig. 7). During the vegetative 
season these roots are laterally displaced, so that 
in course of time the roots of any lobe stand in 
rows forming roughly sectors of concentric circles 
intersecting the circumference of the stock. 
Leaves. 
The leaves of Isoetes Drummondii are pro- 
duced each year in the following sequence : 
foliage leaves, megasporophylls, microsporophylls, 
and the small scale-leaves protecting the apex. 
The half-dozen of so foliage leaves which 
are produced first generally die off during 
the growing season after the sporophylls are 
expanded. The megasporophylls are more 
numerous than the microsporophylls, and usually their laminae are the 
longest leaves formed in the year. Since the microsporophylls are the last 
leaves produced, and are crushed in the centre of the rosette, their sporangia 
often show angular compression, while their laminae may be very short. 
Description of the Sporophyll and Sporangium. 
The lamina of the sporophyll is linear terete, with four large air canals, 
over which the stomata occur ; it has no sderenchyma strands. The leaf 
expands below ground into the usual wide membranous wings. 
The median portion of the sporophyll base from the region of the 
ligule to about the lower end of the sporangium becomes tough and 
cartilaginous towards the close of the vegetative season. This is due to 
an alteration in the nature of the walls of the epidermis on the abaxial 
surface, and, near to the ligule, of two or three layers of mesophyll cells in 
addition. These cells become dark brown and slightly thickened. There 
is thus formed a structure recalling the leaf-base or phyllopodium of Isoetes 
Hystrix or I. Duriaei, but it does not terminate in distal spines nor does it 
involve the base of the leaf to its insertion on the cortex. It forms a tough 
shield-shaped structure, in the concave surface of which the sporangium lies. 
low, at close of vegetative season. 
a, groove ; B, roots of current 
season ; C, root-bearing cortex of 
current season ; d, withered roots 
of previous season ; E, root-bear- 
ing cortex of previous season; F, 
scar surface. 
