IX 



A/AJ^A TTIA CE^—ISOETA CE^ 



IJ7 



early autumn, and continue to do so as long as the conditions 

 permit of growth. The spores are set free by the decay of the 

 sporangium wall, which probably in nature is not completely 

 the case until winter or early spring, which seems to be the 

 natural time for germination. If they are set free artificially, 

 however, they will germinate promptly, especially if this is done 

 late in the autumn or during the winter. Thus spores sown in 

 December produced free spermatozoids in two weeks. The 

 spores do not all germinate with equal promptness, and all 



Fig. 145. — A, Young male prothalliiim of Isoetes setacea (A. Br.) ; v, vegetative cell, X 1280 ; B, two 

 fully-developed male prothallia of /. echinosfiora vaf. Bi-attnii (Durieu), X 1200 ; I, horizontal 

 section; II, vertical section; C, spermatozoid oi I. Malinverniana, X 1480. A and C after 

 Belajeff. 



stages of development may be met with in the same lot. The 

 ripe spore has no chlorophyll, but contains besides the nucleus, 

 albuminous granules, small starch grains, and oil. 



The first division wall cuts off a small cell from one end, 

 which undergoes no further development, and represents the 

 vegetative part of the prothallium, which is here absolutely 

 rudimentary. The rest of the spore forms at once the single 

 antheridium. In the latter two, walls are formed so inclined to 

 each other as to include two upper cells and one lower one 

 (Fig. 145). This latter next divides into two by a vertical 



