FRESH-WATER ALG^ OF THE UNITED STATES. 159 



A. coiiTergens^ Ehrb. 



A. Isevis mediocris," profunde et anguste constrictus, aculeis convergentibus armatus ; semicel- 

 lulis ellipticis vel ovato-oblongis, nonnunquam reniformibus, utroque fine aculeo longo firmo 

 incurvo instructis. (R.) 



X>mm.— 0.00185"— 0.0016". (R.) 



Syn. — A. convergens, Ehrenberq. Rabenhorst, Flora Europ., Algarum, Sect. III. p. 221. 



Bab. — South Carolina ; Georgia ; Florida ; Rhode Island ; Bailey. 



Frond smooth, broader than long ; constriction deep, acute ; segments elliptic, each having its 

 lateral spines curved tow^ards those of the other; ends convex. L. i^g^" — gig'' ^- tiVt" — 

 ,^,". (Archer) 



Family ZYGNEMAOE^. 



Cellulse cylindricse, sequipolares, similes, in familias filamentosas arete conjunctoe, et cytioblasto 

 centrali plasmate plerumque radiante involuto, et plasmate chlorophylloso aut effuso, aut effigurato, 

 aut (plerumque) in fascias spirales ordinato, et granulis amylaceis instructae. Filum simplex. Pro- 

 pogatio fit zygosporis coujugatione cellularum binarum ortis. Conjugatio triplici modo, aut lateralis 

 aut scalariformis vel genuflexa. Vegetatio fit divisione transversali repetita. 



Cells cylindrical, the same at both ends, closely conjoined into filamentous families, furnished with 

 a central cytioblast wrapped up in generally radiating protoplasm, and with chlorophyllous proto- 

 plasm effused in shapeless masses or arranged in spiral filaments, and also with scattered starch- 

 granules. Filament simple. Propagation takes place by means of zygospores, arising from the 

 conjugation of two cells. Conjugation occurring in three ways, lateral, scalariform, and genuflexuous. 

 Growth taking place by means of transverse division of the cells. 



Remarks. — The family under consideration is among the commonest and most 

 widely diffused of all the fresh-water algae. In almost every ditch or spring, or 

 dripping moss-covered rock representatives of it are to be found, so that wherever 

 quiet water is they may be confidently looked for. The single filaments are so minute 

 that frequently the unaided eye cannot distinguish them, but multiplication with 

 them is such a rapid process, that wherever found they are in great masses. These 

 masses, when growth is active, are of a beautiful intense green, glistening and 

 shining with the gelatinous matter which coats the threads and makes the mass so 

 slippery. They may be found in greater or less abundance at all seasons, but as 

 the specific characters are largely of sexual origin, non-conjugating specimens are 

 of little value. For this reason, Zygnemas are only worth gathering when in fruit. 

 The spores appear to be formed only in the spring and early summer, at least these 

 are the only times in which I have found fertile filaments. In this neighborhood 

 I have collected them in excellent condition as early as the beginning of April and 

 as late as the latter part of June. Further south, conjugation of course commences 

 earlier, and fine fruiting specimens received by myself from Mr. Canby were col- 

 lected in Florida by him in February, 



When conjugating freely the mass of Zygnema or Sjpirogyra loses its beautiful 

 bright green color and become dingy and even brownish, often very dirty looking. 

 The collector soon learns to pass by the beautiful vivid mass, as comparatively 

 worthless, and fasten upon the pale, wan, sickly, apparently dying specimens as 

 prizes worthy of a place in his cabinet. 



In the ZygnemacecB the individual plant, as ordinarily considered, is a filament 



