224 Cushman: Zygospores of desmids 



not constant, their use as a basis for any sort of division is at once 



seen to be valueless. ' ^ 



The following forms were found in collections made at Pond- 



ville, in May, 1903 ; South Framingham and Reading, Mass., 



May, 1904. The first two collections were made by the waiter, 



and the last by Mr. G. A. Fisher. . - 



Closterium Dianae Ehrenb. Plate 7, figures 1-3. 



In the series shown, certain definite steps are represented. In 



/. 



truded and united. At this stage it consists of two portions : an 

 outer clear, hyaline mass and an inner more dense portion with 



w , 



many chlorophyl-granules and oil-globules. The outer margin of 

 the clear mass forms a perfect sphere. In the breaking of the 

 cells in the beginning there may be three conditions. They may 

 open as in Ji^. /, but leaving no definite line of breakage across 

 the cell, looking at first glance as if it w^ere more of a stretching 

 than an actual break. This condition was frequently noted. 



In the second condition, as In Jigs. 2 and j (the lower cells), 

 there may be a definite break in the middle, but the two parts re- 

 main attached to one another. In the third case, as in the upper 

 cell oijig.j^ the two portions become entirely separated. This 

 last stage is interesting when compared with the following species. 



In the 



{f^ 



the mass containing the chlorophyl is gathered together at the 

 center, forming a spherical mass about which the hyaline portion 

 forms an outer covering. At this stage it is considerably smaller 

 than at first (Jig. /). In the final stage the chlorophyl mass re- 



I 



mains about the same size as in Jig. 2 and the outer portion forms 

 a thickened wall. 



p 



Specimens in all these three stages were very common in the 

 material collected by Mr. Fisher at Reading. . 



* 



Diameter of the completed zygospore, 36-40//. 



Closterium lineatum Ehrenb. Plate 7, figures 4-6. 



In this species there are two things of especial interest when 

 compared with the foregoing. The cells are completely separated 

 and the semicells resulting adhere in a peculiar manner to the out- 

 side of the hyaline mass, extending directly outward from the sur- 



