43 



thallus. The large cells not containing chlorophyll, 

 on the side next the ground, develop in about thirty 

 hours into the rhizoids. The side exposed to the 

 light becomes the dorsal side. 



SEXUAL EEPRODUCTION. 



The sexual organs of Marchantia are situated 

 upon special receptacles — the male are shield- 

 shaped, with a scalloped outline, the female radiat- 

 ing like bare umbrella ribs. The two sexes are 

 situated upon different plants (dioecious). 



(1) The Male Receptacle consists of a stalk sur- 

 mounted by a flat disc, it is a metamorphosed 

 branch of the thallus. The upper side of the recep- 

 tacle has the same structure as the dorsal surface of 

 the thallus, and the under side has the same struc- 

 ture as the ventral surface, and bears rhizoids and 

 scales. On the upper surface sunk in special cavities 

 are the anther idia. In each cavity is one anther- 

 idium, besides some short unicellular paraphyses. 

 The cavity closes above the antheridium into a 

 narrow canal. The antheridium is a shortly- stalked 

 oval body with a unilamellar chlorophyll-containing 

 wall. It makes its appearance first of all as a papil- 

 liform swelling, this divides into two, the upper 

 becomes the antheridium and the lower the sialk. 

 The upper cell dividing successively by walls at 

 right angles produces a closely aggregated tissue of 

 small square cells ; these are the mother cells of the 



