ANTHERIDIUM OF MARCHANTIA. 



341 



receptacles are readily distinguishable ; the former shield- shaped, 

 with scolloped outline (Fig. 122, A), the latter radiating like 

 bare umbrella ribs. The two sexes are situated upon different 

 plants, i.e., the plants are dioecious ; the receptacles and their 

 stalks are metamorphosed branches of the thallus. 



We prepare between elder-pith delicate longitiidinal sections 

 through the male receptacle, and can determine that its upper 

 side has exactly the same structure as the dorsal surface of the 

 thallus, and that similarly the under side resembles the ventral 

 surface of the thallus, and bears rhizoids and scales. On the 

 upper side, however, sunk in special cavities, are the antheridia 

 (Fig. 123, A). On suitable sections we can see that in each 

 cavity is found only 

 one antheridium, be- 

 sides some short uni- 

 cellular paraphyses 

 (p] ; the cavity con- 

 tracts above the an- 

 theridium into a 

 narrow canal. The 

 antheridium is a 

 shortly-stalked, oval 

 body, with a uni- 

 lamellar chlorophyll- 



contamingwall. The 



FIG. 123. MO/rchantia polyiiiorpha. A , an almost ripe 



Special mother-Cells antheridium in optical cross-section ; p, paraphyses. B, 

 ^t f^- o,-o+ rt spermatozoids (antherozoids), fixed with 1 per cent, osmic 



tne spermato- a id(vl x ^ B x g^ 

 zoids (anthero- 

 zoids) have been produced by successive divisions at right angles, 

 and even in the almost ripe antheridium still form rectilineally ar- 

 ranged cross and longitudinal rows (compare the Figure). Shortly 

 before the ripening of the antheridium, the special mother-cells 

 round off, and become disconnected, the wall of the antheridium 

 ruptures at its apex, and the small, round cells are evacuated. 

 If a drop of water is placed upon a fully-developed receptacle, the 

 water is seen rapidly to spread over its whole surface, and soon 

 becomes milky. If this water is now examined with a high 

 power, we can see in it innumerable evacuated spermatozoidal 

 cells. They remain at rest only a short time, when the cell- 

 membrane swells ; finally it is ruptured, and the spermatozoid 

 escapes into the surrounding water. The spermatozoids are 



