350 GENERAL MORPHOLOGY OF PLANTS 



they were being developed. The gamete plants of Selaginella 

 then are entirely dependent on the spore plant for their food, a 

 condition of things entirely different from that in the other fern 



plants we have studied and in 

 the liverworts and mosses. In 

 one species of Selaginella (S. 

 rupestris) the large spores some- 

 times do not escape from the 

 spore case. The spore case 

 cracks open and some of the 

 small spores from their spore 

 cases above fall in. Here they 

 produce the sperms, and the egg 

 in an egg case (archegonium) is 

 fertilized while the female gam- 

 ete plant is still in the spore 

 case. The embryo develops 

 here also, and when the root 

 and stem emerge, the process is 

 exactly like that of a germinat- 

 ing seed of the higher plants. 

 The large spore case of Sela- 

 ginella then with its large spore 

 comes very near being a seed, 

 and this places Selaginella very 

 near the seed plants. 



THE QUILLWORTS 

 (ISOETES). 



519. General characters. 



The quillworts are peculiar 

 Fig. 339- plants. They grow in very wet 



Isoetes, mature plant, sporophyte stage. placeS) or even part ly or wholly 



submerged for parts of the year. The leaves are long, slender 

 and terete except at the base, which is somewhat spoon-shaped. 

 The bases of the leaves overlap on a very short stem, which is 



