184 FRESH-WATER ALG^E OF THE UNITED STATES. 



Genus SCHIZOMERIS, KTZ. 1 



Thallus filliforrais, cylindricus, hie illic valde contractus, basi attenuata affixus. Vegetatio fit cel- 

 lularura divisione initio in duas postea in tres (?) directionem. Propog.atio fit zoogonidiis. Zoogo- 

 nidia in thalli juvenis cellulis orta, ovata, polo antico ciliis tribus instructa. 



Thallus filiform, cylindrical, here or there strongly contracted, adnate by the strongly contracted 

 base. Growth in the beginning by the division of the cells in two directions, afterwards in three 

 directions. Zoogonidia formed in the cells of the young thallus, ovate, their anterior end furnished 

 with three cilia. 



Remarks. The plant from which the above generic description has been drawn 

 up grows abundantly in our ditches below the city. Whether it really belongs to 

 the genus Scldzomeris or is the representative of a new group is somewhat uncer- 

 tain. I have never seen the European plant, but, if I understand the descriptions 

 of it, the cells in it are all arranged in a single plane. This certainly is not the 

 case in the old plants of our North American form, for in them the cells are so 

 placed as to make a thick opaque filament, the outside of which everywhere pre- 

 sents the outer Avails of cells. The life history of the European species has not 

 been at all worked out, and I have refrained from actually indicating a new genus, 

 in the absence of absolute knowledge upon the subject, because the specific cha- 

 racters of the two plants are so much alike. 



I have had some opportunities for studying the life history of our American 

 plant. The zoospore (Fig. 1 c. pi. XVIT.) is of the ordinary conical or ovate form, 

 with a very decided transparent anterior end, from which arise three cilia. As the 

 number three is a rare one for cilia to exhibit, I have examined several zoospores 

 with care, and am very certain that they had no more or less. It is, therefore, 

 probable that the number is fixed for the species, although just possible that my 

 finding several individuals in agreement was accidental. The zoospore after a 

 period of free life, during which its motion is very active, becomes quiescent, and, 

 its cilia withering away, attaches itself by its smaller end to some twig, stone, or 

 other support. At the same time it appears to change its shape somewhat, grow- 

 ing longer and narrower, and the smaller end spreading out to form a little foot. 

 Simultaneously with these changes the young plant acquires a cellulose coat, and 

 so becomes a perfect cell, in which I have never been able to detect any nucleus. 

 After a while the cell thus formed divides transversely into two, which, of course, 

 lay end to end. Each of these cells then grows until it attains a certain size, and 

 then the transverse division is repeated. In this way the process goes on until 

 finally a long filament is produced, which is composed of but a single series of 

 cells. These cells are much broader than long, and are placed end to end, so that 

 the cylindrical frond is made up as it were of disks laid one upon the other. 

 When the filament has in this way reached a certain stage of development, one of 

 two things occurs, either the cells begin to divide at right angles to the plane of 

 their previous division, or else the production of zoospores takes place. In the 

 first instance each cell divides into two, four, or more cells. This division, I believe, 

 occurs in three if not all directions, so that each original cell is represented by a 

 number of cells, and a sort of compound filament arises, out of which the matured 



