4 -.8 



BOTANY 



PART II 



ruptured, and tlie green iirothalliuni protrudes as a small saddle-sliai)ed liody. 

 On it three archegonia are produced, but only the fertilised egg-cell of one of them 

 develops into an embryo, whose foot, remaining for a time sunk in the venter of 

 the archegonium, finally ruptures it (Fig. 406). The first leaf of the germ plant is 

 shield-shaped (Fig. 403, C), and floats on the surface of the water. 



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

 and spores exhibit a number of distinctive peculiarities. The micro- and macro- 



spit 



Fio. 405. — Sdlrinianntimf!. Peveloimient 

 of the male protliallium. A, Division 

 of the iiiitTosporc into three cells 

 I-III ( X 8(30) ; B, lateral view ; C, ven- 

 tral view of mature prothallium ( x 

 640). Cell I has divided into the pro- 

 thallinm cells a and p ; cell II, into the 

 sterile cells b, r, and the two cells sj, 

 each of which has formed two sperma- 

 tozoid iiiothpr-cells ; cell III, into the 

 sterile cells d, r, and the two cells sj. 

 The cells s,.s-j and sySo represent two 

 aiitheridia ; the cells b, c, d, <•, their 

 wall-cells. (After Belajeff.) 



Fiii. 400. — Salvinla nat<m,'!. Embryo in longitudinal sec- 

 tion ; pr, prothallium ; S, spore-cell ; c, exiniuni ; p, 

 periniiim ; S2^n', sporangial wall ; ar, archegonium ; 

 embr, embryo ; /, foot ; blj, bl.,, 6/3, the first three 

 leaves ; st, apex of stem. (After Prinosheim, x lOn.) 



sporocarps at first develop alike, in each a single macrosporangium is laid down 

 surrounded by the tubular indusium, and from the stalk of the macrosporangium the 

 macrosporangia grow out. In the microsporocarp only the microsporangia develop ; 

 in the macrosporocarp, on the other hand, only the macro.sporangium becomes mature. 

 The numerous spores of the microsporangia are aggregated into several nearly 

 spherical balls or massulae, formed from the interstitial substance derived from 

 the protoplasm of the tapetal cells. Each massula, enclosing a number of spores, 

 is beset externally with barbed, hook-like outgrowths of the interstitial substance 

 (glochidia). On the rupture of the sporangia the massulae are set free in the 

 water, and arc, carried to the macrospores, to which they become attached. In 

 the macrosporangium .32 macrospores are developed but only one comes to maturity ; 



