290 



MORPHOLOGY. 



590. 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. 337. In the inner surface of the expanded base we 

 note a circular depression which seems to be of a different text- 



- 337. 



Base of leaf of isoetes, 

 showing sporangium with 

 macrospores. (Isoetes en- 

 gelmannii.) 



Fig. 338. 



Section of plant of Isoetes engelmahii, showing cup- 

 shaped stem, and longitudinal sections of the sporan- 

 gia in the thickened bases of the leaves^ 



ure 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 remembered that sterile 

 strands of tissue are found in some of the liverworts in the form 

 of elaters. 



591. The spores of isoetes are of two kinds, small ones 

 (microspores) and large ones (macrospores), so that in this 

 respect it agrees with selaginella, though it is so very different in 

 other respects. When one kind of spore is borne in a sporan- 



