4ti6 



BOTANY 



PAKT II 



leaves, and opposite to them two rows of larger, ventral or under leaves. The 

 development of a small, membranous ligule at tlie base of the leaves, on their 

 dorsal side, is characteristic of the Selaginellas. The rhizophores (^'■^^) are organs 

 that are peculiar to the plants of this order ; they are cylindrical, leafless, slioot-like 

 structures, which arise exogenously, usually in pairs, from the stem at a bifurcation 

 (cf. p. 51). At their ends a number of endogenous roots are produced, but the 

 rhizophores are able, when the normal shoots are cut back, to continue their 

 growth as shoots of ordinary construction. Even below the first leaves of the 

 seedling jilant short rhizophores are formed, from wliich the first roots arise 



Fii;. 413. — A, SelaginrUii hehrtica (from 

 nature, nat. .size). B, Selaginelln den- 

 tiridatfi, i.'iiibryonic plant with macro- 

 spore .still attached. (Aftnr Bislhoff, 

 maguified.) 



Fid. 4U. — Selaginella helvetica. A, Macro.spor- 

 angium from above showing tlifi line of dehis- 

 cence ('0- ^, opened, seen from the side ; the 

 four niacrospores, C, have been ejected. D, 

 microsjioianginm in the axil of its sporophyll. 

 A', the same, opened. F, microspores. (x 

 about 15.) 



endogenously. In many species of Selar/inella the epidermal assimilatory cells of 

 the leaves possess, as in Anthoceros, only one large cldoroplast C^"). 



The cones or flowers are terminal, simple or branched, radially symmetrical, 

 or less commonly dorsiventral. Each sporophyll subtends only one sporangium, 

 which springs from the stem above the leaf-axil. The same spike bears botli 

 macrosporangia and microsporangia. Eacli macrosporangium (Fig. 414, ^4- C) 

 contains only four macrospores, which are produced by tlie growth and division 

 of a single spore-mother-cell ; all the other mother-cells originally developed 

 ultimately disappear. On account of tlie increasing size of the spores the 

 spherical macrosporangia become nodular. Opening, which is due to a cohesion- 

 mechanism, occurs along definite lines of dehiscence, the wall splitting into two 

 valves, which curve back from a boat-shaped basal portion. The spores are 

 ejected liy the pressure of tlie contracting boat-shaped part and tlie valves. 

 Numerous spores are formed in the flattened microsporangia. Tlie mode of 



m 



