PRESH-WATEK ALGJ3 OP TKE UNITED STATES. 175 



3 



Family HYDROGASTRE^. 



Plantulas minimEe, terrestres, grcgariaj. Cellula initio globosa, postca clavato- vel pj-rifoi-nii- 

 intumesceiis, basi attenuata elongata et in raniulos subtillissimos hyalinos partita. Cytioplasma 

 iiuiciIagino.sum, tetate provecta gouidia divisiono simultanea trausformatuiu. Cytioderma lamellosum 

 a3tate provecta dilabens et contabescens et gonidia liberans. 



Plants very small, terrestrial, gregarious. Cells in the beginning globose, afterwards clavate or 

 pyriform, with an elongated, attenuated base, divided into very fine, hyaline branches. Cytioplasm 

 mucilaginous, at maturity transformed by a simultaneous division into gonidia. Cytioderui lamel- 

 late, at maturity wasting, withering away and setting free the gonidia. 



Remarks. — The Hydrogastrecu arc curious little unicellular plants, which grow 

 upon wet earth. The matured frond is swollen up at one end to form a subglobular 

 or pyriform head, whilst at the other end it is produced into a long, much-branched, 

 very fine root-like portion -which enters the earth and maintains the little plant in 

 its upright position. The green endochrome is contained almost entirely in the 

 head, and forms generally a coat or layer in the outer portion of its cavity, the inner 

 part of which appears to be occupied by a watery fluid. 



The only specimens which I have seen of this family were found growing in the 

 mud left by the receding water of a recently drawn mill pond, by Dr. Billings, U. S. A. 

 When I got them they were thoroughly dried up, and consequently no opportunity of 

 studying their development was afforded. According to Iviitzing and Braun, the 

 species is propagated ordinarily by the breaking up of the chlorophylous layer of pro- 

 toplasm lining the wall of the cell into a larger number of very small globular spores. 

 These, although not endued with the power of motion, seem from their method 

 of formation and history to be homologous with zoospores. In most cases they 

 are set free by the membrane of the parent-cell becoming gelatinously softened, 

 swelling up, collapsing, and finally dissolving away. The little protococcoid cells 

 then enlarging, develop at one end a hyaline prolongation Avhich penetrates into 

 the ground. Growth and development continuing the upper end of the cell swells 

 up into the ovate or globular head, whilst the lower becomes the hyaline, branch- 

 ing, root-like portion of the new frond. No indication of this method of repro- 

 duction was discoverable in the plants which Dr. Billings sent me. The evident 

 affinities of the family with the Vauclwriacece render it exceedingly probable that 

 there is in it some method of sexual reproduction, as yet undiscovered, allied to 

 that which occurs in the latter. In some of tlie specimens sent me, there were 

 wiiat appeared to be resting-spores (pi. XVI., fig. 2 «), occupying the whole of the 

 cavity of the cell, from which they appeared to be finally discharged by a decay 

 and rupture of the outer coat or wall. How these bodies were formed, and whether 

 they really have power to reproduce the species I cannot tell. 



Genus HYDROGASTEUM, Desv. 



Character idem ac familioe. 

 Characters that of the family. 



H. gr.inulatiim, (Linn.) Pesv. 



H. plerumqne gregarium, scepe aggregatum, baud raro confluens ; cellula e globoso-pyriformi, 

 magnitudine serainis papaveris vel sinapios et ultra, prasino-viridi .superficie pulverulenta. (R.) 



