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. 253). In the RhizocarpecB the pro- 

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

 germinating spore. 



4=86. — 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 



Fro. 253. 



Fig. 352.— A prothallium of a tern, seen from the under side, li, the root-hairs grow- 

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

 root-hairs ; ar, arcliegonia near the apex, x 10. — After Prantl. 



Pig. 853.— Mature antheridium of Adiantum CapUlus- Veneris, p, cells of prothal- 

 lium ; a, wall of antheridium— the sperm-cells are seen escaping, in each a sperma- 

 tozoid is coiled up ; 5, the spermatozoids ; 6, 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. 353). In the other orders the antheridia 

 are not confined to the under surface of the pro thallium j and 

 in some of the RhizocarpecB nearly the whole of the contents 

 of a microspore is developed into one antheridium filled 

 with sperm-cells. 



