386 



BOTANY. 



the cavity of the spore itself, in which, by bending upon itself, it lies 

 at right angles to the axis of the archegonium. The new plantlet 

 bears some resemblance to the embryo in the Dicotyledons ; it has an 

 elongated stem, bearing at its summit two small leaves (cotyledons), 

 having between them a growing bud (plumule) ; at the lower end of 



the stem there is a rudimentary 

 root, and the structure known 

 as the foot, which is common to 

 all Pteridophytes (Fig. 277, //.). 

 The young plant grows from 

 the spore with its cotyledons fore- 

 most (Fig. 277, /. and III.) ; this 

 is only possible by the great 

 bending of the embryo upon 

 itself, for at first its cotyledon- 

 ary extremity points directly to- 

 ward the centre of the spore 

 i.e., away from the opening in 

 the spore- wall. Usually but one 

 plantlet grows from each pro- 

 thallium but occasionally two or 

 more may be developed (Fig. 

 277, J.) 



The adult plant of the asex- 

 ual generation is densely leafy 

 throughout: The leaves are 

 small, moss-like, and are gen- 

 erally placed in four rows, of 

 which two opposite ones are 

 composed of large leaves, and 

 the two intermediate ones of 

 small leaves. Eacli leaf has a 

 small scale-like body, the ligule, 

 on its upper surface at its base. 

 The sporangia occur singly in 

 the axils of certain leaves, gen- 



A, a fertile branch of Selaginella erally in those which form the 

 a, with the quadrangular spore- . ... ., ,. ._. 



bearing spike at the apex ; J5, vertical sec- narrower" fruiting spikes (Fig. 



tion of the spike, showing the microsporau- 070 A\ Mnrro<jnnrnn0-in rrm- 



gia containing microBporea on the left, and ^' 0> A *" angia, o 



the macrosporangia with macrospores on taining four macrospores in 



the right.-.! X 2 ; B x 15. -After Sachs each> U8ually occur in gome defi . 



nite portion of the spike, as nearer the base, or upon one side (Fig. 

 278, B). The microsporangia contain many microspores, and usually 

 also occupy definite positions in the spike. 



But one genus, Selaginella, is known in this order ; it includes 334 

 species of mostly delicate plants, which are mainly tropical, not more 



