WITH NOTES ON OTHKR SPECIES. 115 



swollen apices, usually thickest near the middle, i. e., fusiform ; the later ones arising 

 on lateral branches from below the basal walls of the earlier ones, their successive 

 formation resulting in a sympodial thread with apparently lateral sporangia Zoo- 

 spores ovate or pyriform, at least sometimes, and probably always, apically biciliate, 

 escaping by a single, usually terminal, mouth formed at the apex of a distinct 

 papilla, and immediately becoming encysted and aggregated into a hollow sphere ; 

 after resting, swarming a second time in the laterally biciliate form ; finally encyst- 

 ing again and germinating. Oogonia terminal or intercalary, one- to many-spoied. 

 Antheridia seldom wholly absent, often always present. 



Km/ to recognized Species. 



a. Oogonia with pitted walls b. 



Oogonial walls not pitted c. 



b. Plants diclinous A. prolifera. 



Plants androgynous A. Americana. 



6. Oogonia with smooth walls d. 



Oogonia with spiny walls i. 



d. Plants strictly diclinous A. oblongata. 



Plants at least partly androgynous , e. 



e. Oospores averaging ten or more /. 



Oospores averaging five or less g. 



f. Oogonial branches short ; oospores excentric '. A. DeBaryana. 



Oogonial branches long ; oospores centric A. poltandra. 



g. Oospores over 40/^ in diameter ; antheridial branches much branched A. megaspbbma. 



Oospores less than 40/^ in diameter ; antheridial branches rarely branched h. 



h. Oogonia usually apiculate ; antheridial branches oftenest from the main hypha A. apiculata. 



Oogonia not apiculate ; antheridial branches always from the oogonial branches A. racemosa. 



i. Antheridia on at least some oogonia k. 



Antheridia wholly absent o. 



k. Oogonia usually lateral at the ends of recurved branches A. recurva. 



Oogonia terminal or intercalary, on straight branches I. 



I. Oogonia globular ; antheridia on each one m. 



Oogonia oftenest elliptical ; antheridia not on all n. 



m. Oospores averaging less than five ; antheridial branches very short A. racemosa var. stelligera. 



Oospores averaging more than five; antheridial branches long A. oligacantha. 



n. Oospores 3-12, always globular A. papillosa. 



Oospores 1-3, often elongate A. spinosa. 



o. Oogonia with rather sharp spines ; oospore single A. stellata. 



Oogonia with blunt spines ; oospores one to three A. cornuta. 



