5 i8 



BOTANY OF THE LIVING PLANT 



vestigial vegetative region, and a single antheridium. In certain 

 cases starved Fern prothalli may be found of almost equal sim- 

 plicity. A mucilaginous change appears in the walls of the 

 central mass of cells. Meanwhile their protoplasts form each a single 

 curved spermatozoid, motile in water by two cilia. Swelling of the 

 mucilage by water bursts the wall of the spore, and the spermatozoids 

 escape (Fig. 411, B). 



*US I .^^ ar ..71 ■*- 



Fig. 412. 



Embryology of Selagxnella denticulata, after Bruchmann. I. -III. ( x iai) show 

 germination of megaspore. IV. vertical section of megaspore showing prothallus, 

 archegonia, and embryo {em) with suspensor {sus) ( x 50). V . = a mature archegonium. 

 VI.-IX.=stages of developing embryo. X.=spermatozoids of S. cuspidata, after 

 Belajeff. ( x 250.) 



The germination of the megaspores produces an internal tissue of 

 greater extent, which may be styled the female prothallus. Its 

 development begins below the meeting of the three converging ridges 

 of the tetrahedral spore, and it extends into the spore-cavity, which 

 is stored with nutritive material (Fig. 408). The increase in bulk of 

 the contents ruptures the wall of the spore along the three converging 

 ridges, so that the surface of the tissue is exposed (Fig. 412,1.). Near 

 the central point the first archegonium appears, while laterally others 

 may be formed later, but not in regular succession. A vertical 

 section through a megaspore of 5. denticulata shows it completely filled 

 with tissue of the prothallus, while its exposed surface bears rhizoids 

 (rh) and archegonia in various stages of development (ar) (IV.). The 



