FRESH-WATER ALG^ OF THE UNITED STATES. 181 



remarkable from the fact that, whilst in many cases the little branches which pro- 

 duce the antheridia give origin to the spores also, in others they do not ; so that 

 there are numerous antheridia, which are unconnected with any female organs. 

 When a branch does produce both of the reproductive organs it usually forks into 

 three short branchlets, thus giving origin to a pair of sporangia and a single curved, 

 hooked antheridia. Sometimes, however, there is but a single female branchlet, 

 and I have even seen a sporangium, immediately sessile upon a branch, which at 

 its apex gave origin to a male organ. In the coat of the perfected spore, I have 

 not been able to find more than two distinct strata. 



Figs. 3 and 3 a, pi. 20, represent sporangia and antheridia of this species ; 3 Z>, 

 a simple, young and only partly formed antheridia, magnifi.ed 160 diameters; 3c, 

 a perfected spore magnified 260 diameters. 



V. sericea, Ltngbye. 



V. aquatica vel terrestris, csespitosa, vel sordide vel Isete vel luteolo-viridis ; thallis tennibus, 

 dense intricatis, laxe et vage raraosis, ramisquesaepe adscendentibus vel erectis ; oogoniis ses- 

 silibus vel brevissime pedicellatis, 1-6 seriatis, unilateralibus, oblique et enormiter ovalibus, 

 ore lateral! producto rostellatis ; anlheridiis in thallo ipso juxta oogoniis sessilibus, cylin- 

 draceo-subelavatis, deflexis ; spermatozoideis oblongis, puncto rubro notatis (teste de Bary), 

 in utroque polo cilio unico prseditis. 



Syn. — V. aversa, Hassall, Fresh-Water Algae, p. 54. 



V. sericea, Lyngbye. Rabenhorst, Flora Europ. Algarum, Sect. III. p. 271. 



Hab. — Prope Philadelphia ; Wood. 



Aquatic or terrestrial, occurring in turfy mats of a yellowish, dirty, or bright green color; fronds 

 thin, densely intricate, laxly and vaguely branched, often together with the branches ascending 

 or erect; oogonia sessile or very shortly pedicellate, 1-6 seriate, unilateral, obliquely irregu- 

 larly oval, their lateral mouths produced into a rostellum or beak ; antheridia sessile upon the 

 thallus itself near the oogonium, somewhat cylindrical, subclavate, deflexed especially in age ; 

 spermatozoids (according to De Bary) oblong, marked with a red point and furnished with a 

 single cilia at each end. 



Remarks. — I can perceive no constant differences between V. sericea, Lyng. and 

 V. aversa, Hass. The extreme forms differ somewhat, but both are very common 

 about Philadelphia, and everywhere grade into one another. Prof. Rabenhorst 

 thinks that the two forms are scarcely distinct, and states that the most character- 

 istic differences are, that in V. aversa, the thallus is much thicker, and the oogonia 

 larger and more erect, whilst the oospores are smaller and consequently do not fill 

 the cavity of their case. These differences are, except the last, simply differences 

 in size, and seem to me to depend simply upon circumstances of growth. The rela- 

 tively smaller size of the spore is a very frail hook indeed to hang a species upon. 

 The plant grows in springs and actively running water abundantly in this neigh- 

 borhood ; also on very wet ground, especially on that which is habitually overflowed, 

 such as the face of dams, neighborhood of springs, &c. In the water, it is frequently 

 on the ground, but also often clothes such objects as stones, largish sticks, &c. 



Order jVematophycese. 



Algae multicelnllares, chlorbphyllosoe, membranaceae vel filaraentosae, ramificatione aut instructse 

 aut destitute. Propogatio fit aut oosporis aut zoogonidiis, sed nunquam conjugatione. 



