136 



THE BIOLOGY OF A PLANT. 



nences occurring upon the posterior part and the under side of 

 the prothallium, often among the rhizoids. AVhen fully formed 

 (Figs. TO, 71) an antheridium consists of a mass of rounded cells 

 (xp<>i>)iurt<>zoi<l mother-cells) enveloped by a membrane one cell 

 in thickness. 



,,,-;, :-'.;, 



FIG. 70. (After Suminski, slightly modified.) Adult prothalliura of Ptcris serrulata 

 seen from below, showing the rhizoids (r) at the posterior end, the depression at 

 the anterior end ; the cushion near the latter bearing (in this case) four arche- 

 gonia. Among the rhizoids are the (spherical) antheridia. The chlorophyll- 

 bodies only' are shown in the cells of the broad plate of tissue constituting the 

 prothallium. Just above the anterior depression is seen a prothallium of the 

 natural size. 



FIG. 71. (After Strasburger.) Mature an- 

 theridium of Pteri* xrrntlata. p, periphe- 

 ral cells; i, mother-cells of the sper- 

 matozoids. 



FIG. 72. Diagram to illustrate the ori- 

 gin of an antheridium. A, very 

 young stage; B, older; a, original 

 epidermal cell enlarged ; It, mother- 

 cell of the entire antheridium. 



