754 



PHYSIOLOGY. 



(fig. ?90). The antheridia contain a number of small cells 

 called generally pollen-spores or small spores (fig. 791), which 



Fig. 1103. 



Fig. 1104. 



Fig. 1105. 



OOO G-, 



© © 



2^tgr, 1103. Small spore, poUen-spore, or microspore, of a species of Selagi- 

 nella, bursting and discharging small cells, c, in which spermatozoids 



are contained Fig. 1104. Large spore, macrospore, or megaspore, of a 



species of Selagindla. The outer coat of the spore has been removed to 

 show the entire inner coat, with the young pro-tliallus,p, at the upper end. 



Fig. 1105. Vertical section of a portion of the pro-thallus of the above 



in a more advanced state, showing the archegonia. a. Archegonium, in 

 which the embryo e, has been developed from the germ-cell it contained, by 

 contact with the spermatozoids. This embryo, by the growth of the sus- ; 

 pensor, is forced downwards and imbedded in the upper part of the cellular 

 mass of the spore-sac. 



enclose spermatozoids (fig. 1106). The pistillidia sporangia 

 (fig. 794, b) contain commonly but one spore (fig. 792), called 

 an ovulary spore, large spore, or megaspore. In their organs of 

 fructification the plants of this order closely resemble the 

 Lycopodiaceffi (see p. 374). Like the Lycopodiaceae also, 

 the large spores produce a pro-thallus in their interior (fig. 



Fig. 1106. 



f. 



s. 



©*© 



Fig. HOC. Pollen-spore, small spore, or microspore, of Pill-wort (.Pilularia 

 glohttlifera), bursting and discharging small cells enclosing spermatozoids. 

 Some of the latter may be observed to have escaped by the rupture of the 



small cells in which they were contained Fig. 1107. Vertical section 



of the pro-thalius of tiie above, which is formed, as iu the Lycopodiaceae, 

 in tlie interior of the large sjiore or viegasporc. Only one archegonium, a, 

 is here produced in the centre. The archegonium consists of an intercel- 

 lular canal, leading into a sac below, in which may be seen a solitary germ 

 or embryonal cell. 



1107), in -which subsequently only a single archegonium gene- 

 rally ajjpcars (fig. ] 107, a), as in Pilularia and Marsilca, 

 although iu iSalvinia there are several archegonia formed. Im- 



