428 



PART III. THE CLASSIFICATION OF PLANTS. 



The relative distribution of the two kinds of sporangia presents some varia- 

 tion. As a rule both kinds of sporangia are present in the same cone, so tht 

 it may be described as consisting of microsporophylls and macrosporophylls; 

 in this case there may be several macrosporophylls at the lower part of the 

 cone, or only a single one. 



The spores are developed in fours from the mother-cells resulting from the 

 growth and multiplication of the archesporial cells. They are developed 

 tetrahedrally : but in the macrosporangium usually only one of the mother- 

 cells undergoes division to form spores. The structure of the spores is 

 normal. 



The roots are all adventitious and endogenous. In - some species (P.O. 

 S. cuspidata and Wildenovii) they spring directly from the lower surface of the 



stem at the points 

 where branching 

 takes place. In other 

 (e.g. S. Martensii and 

 Kraussiana) cases 

 they spring from 

 near the apex of the 

 rhizophores after the 

 rbizophores have 

 reached and entered 

 the soil. The roots 

 branch monopodi- 

 ally. 



General Histology. 

 The stem is, in some 

 species (S. spinulosa 

 and denticulata) mo- 

 nostelic, but in most 

 species it is poly- 

 stelic (two or three). 

 The epidermal and 

 the fundamental 

 tissue of the stem 

 is prosencbymatous, 

 without intercellular 

 spaces. In corre- 

 lation with this each 

 stele is suspended, 

 by delicate trabecular 

 cells developed from 

 the endodermis, in 



an air-chamber: each vascular bundle going to a leaf is in a similar chamber 

 which communicates in the lamina with the external air through the stomata. 

 Each stele is surrounded, towards the air-chamber, by a pericycle consisting of 

 one or sometimes two layers of cells. The stele is diarch, or polyarch, circular 

 or oval in transverse section, the wood-bundles joining in the centre. 



'"'IG. 278. Prothallium and embryo of Selaginella Martensii 

 (x '65: after Pfeffer): s coat of macrospore ; p prothallium ; 

 o arcnojfonium ; d-d diaphragm ; end so-called endosperm : R 

 an embryo (there is a smaller one to the right): s suspensor; 

 c c developing cotyledons; st stem ; v origin of the root; / so- 

 called foot. 



