ISOETES 151 



chambers separated into compartments by 

 numerous diaphragms. 



(e) Make a drawing (X 2) illustrating the features 

 mentioned in 4, (c) and (d). 



(/") Make a cross-section of the blade near the 

 middle, and note the number of air chambers 

 surrounding the vascular bundle. 



(g) Make a diagram, 10 mm. in diameter, showing 

 the leaf -structure in cross-section. 



(ti) On plants which grow under water no stomata 

 occur, but they are present on leaves that grow 

 exposed to the air. Are stomata present in 

 your specimen? If so, make a drawing of 

 two or three, each 15 mm. in longest diameter. 



(i} Study carefully the expanded base of this leaf, 

 noting the membranous margins. 



(k) Directly above the leaf-insertion, and on the 

 ventral (inner) surface, observe the cavity or 

 pit (fovea), containing the single sporangium. 



(/) Note the thin membrane (velum) extending 

 over the sporangium. The velum is formed by 

 the projection of the margin of the fovea. It is 

 absent in some species, and in /. lacustris it 

 does not completely cover the sporangium. 

 In terrestrial species there is no opening through 

 it. State the shape and location of this open- 

 ing in your specimen, using a hand lens for the 

 observation. 



(m) Above the fovea find a flat, membranous out- 

 growth, the ligule. Describe its shape and 

 state toward which end of the leaf it projects 

 The slightly swollen base of the ligule is in- 

 serted in a depression (f oveola) , smaller than the 

 fovea and directly above it. This last point is 



