SECT. I 



CRYPTOGAMS 



111 



them develops into an embryo, whose foot, remaining for a time sunk 

 in the venter of the archegonia, finally ruptures it (Fig. 345). The 

 first leaf of the germ-plant is shield-shaped (Fig. 342, (7). 



The development of Azolla proceeds in a similar manner, but the sporangia 

 and spores exhibit a number of distinctive peculiarities. The numerous spores of 

 the mierosporangia are aggregated 

 into several nearly spherical balls 

 or massulse, formed from the inter- 

 stitial substance derived from the 

 protoplasm of the tapetal cells. 

 Each massula, enclosing a num- 

 ber of spores, is beset externally 

 with barbed, hook -like out- 

 growths of the interstitial sub- 

 stance. On the rupture of the 

 sporangia the massuhe are set 

 free in the water, and are carried 

 to the macrospores, to which 

 they hook themselves fast. A 

 sporocarp contains one macro- 

 sporangium, in which only a 

 single macrospore comes to matu- 

 rity ; in the course of its develop- 

 ment it supplants all the other 

 spore-rudiments, and finally the 

 sporangial wall itself becomes 

 flattened against the inner wall of 

 the sporocarp, frequently under- 

 going at the same time partial 

 dissolution. The macrospore is 

 enveloped by a spongy perinium 

 whose outer surface exhibits 

 numerous depressions and pro- 

 tuberances prolonged into fila- 

 ments. At the apex of the spore 

 the perinium expands into three 

 pear - shaped appendages, while 

 the upper part of the ruptured 

 sporangium remains attached to the spore in the form of an umbrella-like expansion. 

 The formation of the prothallia is effected in essentially the same way as in Sal- 

 vinia, except that only one antheridium with eight spermatozoids arises on each 

 of the small male prothallia protruding from a massula. 



In the case of the Marsiliacme the prothallia are even more reduced, but other- 

 wise their mode of development is very similar. Each of the minute female 

 prothallia formed at the apices of the macrospores produce a single archegonium. 



The sporocarps of the Marsiliaceae have a more complicated structure : those of 

 Pilularia globulifera are divided into four chambers, each with a single sorus ; in 

 Marsilia they enclose numerous soil (14-18) disposed in two rows. The sori in 

 both genera contain both micro- and macrosporangia, while those of the Salviniaceae 

 are always unisexual. 



Fig. 345. — Salvinia natans. Embryo in longitudinal sec- 

 tion ; pr, prothallium ; S, spore-cell ; e, exinium ; p, 

 perinium ; spw, sporangial wall ; ar, archegonium ; 

 embr, embryo ; /, foot ; Hj, M2, &Z3, the first three leaves ; 

 st, apex of stem. (After Peingsheim, x 100.) 



