118 PALMELLACEtE. 



of large size, from which they radiate. Afterwards they become detached, and then each 

 is seen at the end of a mucous prolongation similar in appearance to tliat already 

 noticed as occurring in Gloeocajysa. Mr. Thwaites compares these threads to the 

 mycelium of a fungus, but regards the increase of cells by cell-division as properly an 

 act of gemmation and not of true reproduction. The reproductive process in these 

 plants is by conjugation of two cells, which takes place in a manner similar to that 

 already noticed as occurring in Zygnemacece. A narrow connecting tube, soon enlarg- 

 ing to the breadth of each cell, is formed between two contiguous cells, through which 

 the contents of both cells are mixed together ; and thus a sporangium filled with a 

 denser and more distinctly granular endochrome is formed, the membranes of the 

 original cells being absorbed in the process. Probably at a future stage the contents 

 of this sporangium are resolved into zoospores. (See Thw. An. Nat. His. ser. 2, vols. 

 2 and 3.j 



Higher in structure than Palmella, and showing some approaches to the JSFostochinece, 

 or even to the gelatinous CONFERVACEiE (Chcetophora) is Hy drums, the only genus 

 which we shall further describe. 



I. HYDPvURUS, Ag. 



Frond fixed at base, cylindrical or compressed, elongated, branched, gelatinous. 

 Structure : seriated, but separate, cellules, filled with bright-green endochrome, enclosed 

 in gelatinous parallel tubes, ranged longitudinally in the frond, and surrounded by a 

 common gelatinous envelope. 



Of this genus several species have been described by authors, all having a close 

 resemblance to each other, and all very variable in ramification. Indeed it is almost 

 impossible to fix characters by which they can be permanently kept apart ; and instead 

 of adding another specific name to the already too numerous list, I prefer to consider the 

 American specimens received as constituting a luxuriant variety of the best known of 

 the established species. All previously recorded species or varieties of these plants are 

 natives of rapid rivers and streams in various parts of Europe. 



1. Hydrurus penicillatus, var. occidentalis, Harv.; frond very long (1-2 feet or 

 more) much branched ; branches very irregular, scattered or crowded, wormlike, taper- 

 ing to a fine point, naked or clothed with feathery villous ramuli ; cells ellipsoidal or 

 pearsliaped, twice as long as their diameter. 



Hab. On the rocky bottom of rivers and streams, in a strong current. Santa Fe, 

 New Mexico, 3Ir. Fendler, February to April, 1847. (v. s. in Herb. T.C.D.) 



