2 34 Rhodora [December 



Division in Desmids under Pathologic Conditions. — In 

 looking over certain desmid material during the past summer a char- 

 acter was noticed which to my knowledge has not been called to 

 notice in any published paper. It is a well known fact that the 

 microscopic plants, Desmids, Diatoms, and other small or unicellu- 

 lar algae furnish a considerable amount of the food supply of various 

 small fresh water animals. The effect upon the plant cell in such a 

 case is peculiar. In several cases in material obtained from Read- 

 ing and South Framingham, Massachusetts, there were also in the 

 bottles various Entomostraca, the two genera bearing upon the mat- 

 ter in hand being Daphniaand Cypris. These 

 small Crustacea have bivalve shells which are 

 transparent, allowing the food to be seen after 

 it has entered the digestive tract. It was 

 noted that the change was not always imme- 

 diately fatal to the Desmid that was swal- 

 lowed. In a number of cases the cell had 

 not only continued to live but had continued 

 to carry on its division. In such cases, how- 

 ever, instead of the newly formed cells being like the old cells as is 

 the usual condition, they appeared as contorted and bizarre forms 

 quite unlike the old semi-cells. This is of course due in some way 

 to the action of the chemical contents of the digestive tract upon the 

 cells of the plants, thus causing truly pathologic conditions. It was 

 noted in three genera, Cosmarium, Euastrum and Micrasterias, that 

 such conditions occurred. The last, of which a figure is given, fur- 

 nishes perhaps the best example of deviation from the typical form. 

 The end lobe is fairly typical in its general shape but has an addi- 

 tional small lobe on the face. The lateral lobes are not as well 

 marked, being on one side almost entirely fused, on the other less 

 so. In both cases there are various additional smaller lobes. Alto- 

 gether, if broken away from the old semi-cells, it would never be 

 taken for a semi-cell of Micrasterias papillifera^ which it neverthe- 

 less is. It would be interesting to determine the sort of form that 

 would be produced if these peculiar cells were to divide again. Some 

 clue as to whether or not these cells would exert an influence on the 

 semi-cells derived from them, might perhaps be obtained from actual 

 experimenting. — Joseph A. Cushman, Boston Society of Natural 

 History. 



