160 



MANUAL OF BOTANY 



Fig. 918. 



Ferns than the Lycopods ; its embryogeny, the hypobasal cell 

 not giving rise to a suspensor ; the isolated position of its 

 sporangia, and the form of its antherozoids. On the other hand, 

 it shows relationship to the Lycopods in the occurrence of the 

 sporangia on the upper surface of the leaf near the base ; in the 

 peculiar features of the'gametophyte arising from the macrospore, 

 which approaches the condition obtaining in the Gymnospeims 

 even more closely than that of Selaginella ; in the occurrence of 

 a peculiar outgrowth of the leaf close to the sporangium, which 

 is shared only by Selaginella ; and in the structure of its apical 

 meristem. The adventitious nature of the first root also 

 supports this view of its position. 



The heterosporous Ly- 

 copodinae have sometimes 

 been called the LigulatcB, 

 from the occurrence of the 

 particular outgrowth re- 

 ferred to, which is known 

 as the ligule. Selaginella 

 is the best kno^vn repre- 

 sentative, and in many 

 respects is the highest type 

 represented in the group. 

 Its form shows more 

 variety than that of any 

 other genus ; the stem is 

 slender, herbaceous, and 

 sometimes erect, some- 

 times creeping ; almost 

 always showing a bilateral 

 symmetry, which is very 

 evident when it is much branched ; the branches spread out in a 

 flattened manner, and show an evident difference between the 

 upper and under sides. The branching is apparently dichotomous 

 and the stem a sympodium. Eecent investigations tend to the view 

 that the dichotomy is only apparent, and that it is reaUy lateral. 

 The stem bears numerous small leaves of very simple struc- 

 ture. They are arranged in pairs, which are of unequal size, one 

 leaf being much smaller than the other. The successive pairs 

 decussate with each other, and in many cases, by some distortion 

 in growth, the small leaves come to lie on the upper surface of 

 the stem, while the larger ones are on the lateral flanks {fig. 918). 

 Each leaf bears the peculiar ligule spoken of above. 



Fig. 



918. Selaginella helvetica, s. 

 Small leaves of upper surface, 

 leaves of lateral flanks. 



Stem. 0. 

 u. Larger 



