Algal Genera Acicularia and Acetabulum 329 



this constriction is not so pronounced as in the case of the sterile 



branches. The young sporangia are at first abundantly free from 

 each other. They are at an early stage short-cylindrical or some- 



what club-shaped, with a rounded-obtuse apex (Figs, 12, 13, 15), 

 but a little later, when they come to be coherent laterally, each 

 has a free apex that is decidedly conical or conico-mammillate 

 (Fig. 19). While, however, the disc is still very small, the end of 

 the sporangium broadens out and nothing but a small mucro re- 

 mains to represent the conical apex of the earlier stage, and even 

 this mucro is sometimes obscure or obsolete. The hypopeltal 

 process (segment of the corona inferior of Solms-Laubach) origi- 

 nates a little later than the sporangium. It begins as a broad 

 dome- shaped outgrowth involving the whole region between the 

 base of the sporangium and the vestibule -wall. Its further devel- 

 opment offers nothing worthy of special comment unless it be the 

 fact that it becomes strongly emarginate or emarginate-bilobed. 

 That the hypopeltal process bears neither polytomous filaments 

 nor the rudiments of them is well understood. It has already 

 been noted that the rudiments of the polytomous filaments at the 

 time of their emergence from the previously undifferentiated 

 primordial ray are terminal in position. Later, however, the 

 region just below them on the side toward the sporangium grows 

 out into what is finally the emarginate or emarginate-bilobed apex 

 of the coronal process. In reality, the organic apex of the ray as 

 a whole is doubtless still to be found somewhere between the 

 points of insertion of the two polytomous branches or their rudi- 

 ments, having been thrust into an apparently lateral position by 

 the development of the three superposed lateral outgrowths, 

 namely, the sporangium, the hypopeltal process, and the terminal 

 portion of the coronal process. The developmental history of the 

 ray thus forces us to accept in the main the views of Solms-Lau- 

 bach in regard to the morphological homologies of the disc and 

 its parts, as opposed to the views of Falkenbe 

 Willed The whole disc or cap (including spors 



t 



np-ia. coronal and 



*Falkenberg, P. Schenck, Handbuch der Botanik, 2: 270. 1882. 



t Cramer, C. Denkschr. Schweiz. natf. Gesellsch. Zurich, 30.— (35)- l88 7- 



JWille, N. Eogler & Prantl, Die naturlichen Pflanzenfamilien, i 2 : I5 2 " I 59- 



1890. 



