358 SELAOINELLA. 



S. spinosa, where the leaves are all alike and are spirally 

 arranged, but most of the species correspond to the type 

 described below. The species most commonly cultivated 

 are S. Martensii and S. Kraussiana ; if possible, obtain 

 specimens of both. 



506. General External Characters. In a good- 

 sized portion of one of the above exotic species, obtained 

 from a greenhouse, note 



(a) The profuse branching of the relatively slender 

 but wiry stem, which takes place in one plane and is 

 apparently dichotonious (forking) but really monopodial. 



(6) The small simple leaves, single -veined and more or 

 less lance-shaped, arranged in four rows (two side rows 

 and two dorsal rows) closer inspection shows that the 

 leaves are in pairs, each pair consisting of a larger lateral 

 (strictly speaking, ventral) leaf and a smaller dorsal leaf 

 opposite to it. 



(c) The roots, arising singly at the points of branching 

 of the stem the first portion of the root is stiff, green or 

 brownish, and unbranched, and is often termed the 

 rhizophore, but on reaching the soil (over which the 

 stem grows in a straggling and ascending manner) it 

 divides into numerous slender white branches which are 

 apparently dichotonious. 



(d) The cones, which show radial symmetry, unlike 

 the dorsiventral symmetry of the rest of the shoot, and 

 bear spirally arranged leaves (sporophylls), forming four 

 longitudinal rows and being all alike in size. 



(e) The sporangia, of which there are two kinds, 

 seated singly in the axils of the sporophylls, and seen on 

 turning these down the megasporangia, confined to the 

 base of the cone, and each containing four large rounded 

 megaspores these cause the megasporangium to be 

 lobed and therefore easily distinguished with the naked 

 eye from the smaller and more nearly spherical micro - 

 sporangia, which occupy the upper portion of the cone 



