38 THE AMERICAN MONTPILY [February, 



common with other famiHes of algas, some of the desmids {Etiastrum 

 for example) present the phenomena of polarization to some extent. 

 But as far as structure is concerned, from an optical point of view, it is 

 a very simple study in biology. We are at our A, B, C's. This is 

 primer work in the vegetable kingdom. You can hardly get any lower 

 down. The lichens and fungi are the only things beneath. Of all the 

 green things upon the earth, let me say again, the desmids are among 

 the very simplest. 



But when you j^ass from their structure to their inotion a difficult 

 problem presents itself. This motion is of three kinds. There is the 

 flow of the protoplasm ; the twisting or swarming of little granules in 

 the vacuoles of some genera and in the body of the cell or semi-cell 

 in others, at certain stages ; and the motion of the plant, as a whole, 

 resulting in change of place. And of neither of these can any satis- 

 factory explanation be given ; all that can be done is to state the facts 

 and describe the several movements respectively. The flow ot the pro- 

 toplasm seems to be a true cyclosis or circulation extending over the 

 whole cell or semi-cell ; the dancing of the granules in the vacuoles of 

 Closterhim is local, and is apparently pi'oduced by the general flow ; 

 the swarming of the little bodies in Cosmarlutn and other genera is also 

 local, but not connected with the circulation, as it is not always present. 

 It appears when the plant is at its fullest life, and would seem to be re- 

 lated to reproduction. The external motion is a slow sailing, and is 

 not characterized b}' the definiteness of direction so marked in diatoms, 

 the desmid frequently turning half-way or completely around as it moves 

 across the field. The dancing granules at the ends are confined, so far 

 as I know, to Closteritim^ Pcniiim^ and Dociditini^ and the swarming 

 is most pronounced in Cosmariiiin and Eiiastruin. In j\licrasfc?'ias 

 and Eiiastritju vou will sometimes find black bodies of considerable 

 size scattered over the interior of the cell. In a gathering of large 

 specimens of these genera made during the past summer and that of 

 the previous year they were very distinct. What their purport is no 

 one appears to know. 



Reproduction is by both subdivision and conjugation. In the first 

 process each semi-cell forms the counterpart of itself. These may re- 

 main attached for a time and up to a certain number, as in Docidium 

 or Micrasterias^ where we may have from two to twenty cells in a ro^v, 

 or they mav keep togetlier until the period of conjugation, forming the 

 filamentous desmids. In conjugation, which is a true generative pro- 

 cess, two cells separate each into two valves, and the contents of both 

 fuse and fornr a zygospore. In the filamentous species a connecting 

 tube unites the cells, and the contents of one pass entirelv over into the 

 other and form the spore. Wolle says that the germination of the spore 

 is very rarely detected. I, for one, have never observed it. although 

 the desmids have been constantly under my eye for years. Germina- 

 tion is said to occur in the spring and the result is a copv of the parent ; 

 in Cosmariiim the spore is said to produce a number of such like 

 forms. Tlicre is a chance here for the student to add to our knowledge, 

 but it would appear to be slight. So much for the life-historv of the 

 desmids ; next we come to the classification. 



