370 



BOTANY. 



and is generally provided with root-hairs on its under sur- 

 face, by means of which it secures nourishment for its inde- 

 pendent growth (Fig. 252). In the RUzocarpece the pro- 

 thallium is so reduced as to be only a small outgrowth of the 

 germinating spore. 



486. Both kinds of sexual organs usually occur upon the 

 same prothallium. The antheridia consist of a few or many 

 sperm-cells, which may or may not be surrounded by a wall 



FIG. 252. 



FTG. 253. 



Fig. 252. A prothallium of a fern, seen from the under side, h, the root-hairs grow- 

 ing from the basal end of the prothallium ; an, the antheridia scattered among the 

 root-hairs ; ar, archegonia near the apex. X 10. After Prantl. 



Fig. 253. Mature antheridium of Adiantum Capillus-Vensris. p, cells of prothal- 

 lium : a, wall of antheridium the sperm-cells are seen escaping, m each a spenna- 

 tozoid is coiled up ; g, the spermatozoids ; b, the protoplasm of the sperm-cells still 

 attached to the spermatozoids. x 550. After Sachs. 



of other cells. In the Ferns (Filices) they are few-celled 

 bodies, which project from the basal portion of the under 

 surface of the prothallium ; one of the interior cells becomes 

 divided into sperm-cells, in each of which is a spirally coiled 

 spermatozoid (Fig. 253). In the other orders the antheridia 

 are not confined to the under surface of the prothallium, and 

 in some of the Rliizocarpece nearly the whole of the contents 

 of a microspore is developed into one antheridium filled 

 with sperm-cells. 



