148 FRESH-WATER ALG.E OF THE UNITED STATES. 



b. CORNICULAT.E. Antheridia bent in the form of a horn or a 



hook, placed on the short and bent side-branches of the 



thallus. Brown pigment in the middle of the 



mature oospore. 



aa. tiessiles. Oogonia sessile (or with exceedingly short stems) 



beside the antheridia on the thallus. 



5. V. Dillwynii, Ag. 



6. V. sessilis, Vauch. 



bb. Racemosce. Antheridia at the end of a fruit branch, which, 

 somewhat lower down, carries the oogonium. 



Oogonia turned upward. 



i 



Antheridia and oogonia bending in opposite planes, forming an 



angle with one another. When the oospores fall they are 



surrounded by the oogonium membrane, which is 



not changed to mucus. 



7. V. geminata, Walz. 



8. V. hamata, Walz. 



Antheridia and oogonia (mostly) bending- in parallel planes, the 

 oogonium membrane turns to mucus and dissolves. 



9. V. terrestris, Lyngb. 



Oogonia turned downwards. 



10. V. uncinata, Kg. (Not represented.) 



c. Antheridia straight, with the top covered, and a pair of 

 fruiting tubes standing out at the side. 



11. V. DeBaryana, Woron. (Not represented.) 



t 



B. Between the antheridia and thallus itself is found a shorter empty 



boundary cell. 



a. - - ANDROPHOR^E. Several horn-shaped, bent autheridia 

 placed on a swollen cell containing chlorophyl, which is 

 fixed to the side of the thallus, by means of the boun- 

 dary cell. (Not represented.) 



b. PILOBOLOIDE^E. Antheridia bordering immediately on the 

 boundary cell. (ISTot represented in the United States.) 



c. Place of the antheridia or boundary cell uncertain. 



12. V. tuberosa, A. JBr, 



13. V, JMlus, Mart, 



