FRESH-WATER ALG^ OF THE UNITED STATES. 197 



A. rarely setigerous ; articles 2-8 times longer than broad ; oosporangia mostly single, rarely 

 geminate, subovate, in the lower portion broad, in the middle swollen, in the upper part con- 

 tracted ; the 2 lateral pores situated above the middle ; oospore subglobose or broadly 

 ovate, its coats without markings; antheridia generally bicellular, sometimes tricellular, 

 numerous, placed generally upon the female filament either upon or below the oosporangia. 



Eemarks. — This species was found growing in a rather stagnant brook in the 

 meadow by "Robinson's Knoll," at the junction of the Schuylkill River and Wissa- 

 hickon Creek, near Philadelphia. The filaments, which vary very greatly in size, 

 are in their early history attached to dead leaves and sticks, but finally, I think, 

 float free in the water. The larger, fruit-bearing filaments are remarkable for their 

 crookedness. None of the threads that I have seen ended in a seta-like portion. 



The fruit is produced in abundance, but very rarely is there more than a single 

 spore in any one place. The method of the formation of the sporangia differs from 

 that of all the other CEdogonia which have come under my notice. Instead of 

 two cells being concerned but one cell is employed. The cell (fig. 2 a, pi. 18) that 

 is to be used for such a purpose grows much beyond the ordinary size, until it is 

 nearly or quite twice as large as its neighbors. All the time it is well filled with 

 chlorophyllous protoplasm. This now contracts and finally is all packed into the 

 upper half of the cell. At or even before this time the lateral openings become appa- 

 rent. There are two of them, situated just in the angle where the cell at its upper 

 end commences to contract to the size of its fellow. At this time I think fertiliza- 

 tion takes place, although I have never actually seen the spermatozoids enter the 

 orifices. The cell (fig. 2 h, pi. 17) now divides into two by forming a wall separa- 

 ting the lower empty half from the upper full one, which is to be the sporangium. 

 The contents of the latter now condense into a ball, and it itself becomes more tumid 

 in the middle. Finally a reddish-brown broadly globular spore (fig. 2 c, pi. 18) 

 is formed. I have not been able to make out more than one distinct thick coat. 

 The surface of the spore is smooth. The androspores are formed in a cell (fig. 

 2 d, pi. 18) which has grown beyond the normal size and then divided into four 

 or five short cells, each of which gives origin, I believe, to a single androspore 

 in its interior. The antheridia are numerous, from 2 to 6 being commonly attached 

 to the lower portion of the sporangium, or to the cells just beneath it. They 

 (fig. 2 e, pi. 18) have a rather large foot, and are generally curved at the base. The 

 distal of the two cells composing them is crowned with a little cap, and produces 

 one or sometimes two spermatozoids. These (figs. 2 & and 2 g, pi. 18) during their 

 escape are always very much squeezed out of shape, but when free become globular 

 or slightly pear-shaped. They are highly transparent and contain a few green 

 granules. Their motion is at first slow, but soon becomes very active. The mode 

 of egress from the cell is obtained by the cutting off of the upper end of it, the 

 little cap opening like a trap-door. After this cell has been emptied, sometimes a 

 second similar one is formed, which bears it aloft. I have never seen spermato- 

 zoids produced by this second cell. 



A. Huntii, Wood. 



Filuma plerumque in setam longam, terminalem coloris expertam productum ; oogoniis pler- 

 nmque singulis, globosis, interdum nonnihil hexagoniis, medio nonnihil tumidis, poro laterale 



