290 



MORPHOLOGY. 



590. Sporangia of isoetes. — If wc 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 exijanded base ive 

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



Fig. 337. Fig-33S. 

 Base of leaf of isoetes, Section of plant of Isoetes engelmanii, showing cup- 

 showing sporan,t<ium with shaped stem, and longitudinal sections of the sporan- 

 macrospoi-cs. (Isoetes en- gia in the thickened bases of the leaves, 

 gelmannii.) 



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 jilants 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 selaginclla, ihoiigli it is so very different in 

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



