QUILLWORTS. 



I8l 



leaf to a quill. Fig. 155 represents one of these quillworts 

 (Isoetes engelmannii). The leaves are the prominent part of the 

 plant, and they are about all that can be seen except the roots, 

 without removing the leaves. 

 Each leaf, it will be seen, is long 

 and needle-like, except the basal 

 part, which is expanded, not very 

 unlike, in outline, a scale of an 

 onion. These expanded basal 

 portions of the leaves closely 

 overlap each other, and the very 

 short stem is completely covered 

 at all times. Fig. 157 is from 

 a longitudinal section of a quill- 

 wort. It shows the form of the 

 leaves from this view (side view), 

 and also the general outline 

 of the short stem, which is tri- 

 angular. The stem is therefore 

 a very short object. 



297. Sporangia of isoetes. — 

 If we pull off some of the leaves 

 of the plant we see that they are 

 somewhat spoon -shaped as in 

 fig. 156. In the inner surface 

 of the expanded base we note a 

 circular depression which seems 

 to be of a different texture from 

 the other portions of the leaf. 

 This is a sporangium. Beside 

 the spores on the inside of the 

 sporangium, there are strands of 

 sterile tissue which extend across 

 the cavity. This is peculiar to isoetes of all the members of 

 the class of plants to which the ferns belong, but it will be re- 



Fig. 155- 

 Isoetes, mature plant. 



