222 



METHODS IN PLANT HISTOLOGY 



will give beautiful preparations. A deep stain with phloxine and a 

 rather light stain with anilin blue is better for the pyrenoids and nu- 

 cleus, while a light stain in the red and a deep stain in blue is better for 

 the chromatophores. 



Material may be fixed and stained as directed for Volvox. Formalin 

 8 C.C., acetic acid 2 c.c, and water 90 c.c. fixes well, and material may 

 stain in the solution indefinitely. 



Fig. 47. — Some common desmids. A and B, Clostcrium conjugating; C-F, Cosmarium; C and 

 D, adult cells; E and F, dividing; the inner half-cells will grow until they reach the size of the 

 outer half-cells; G, Micrasterias. A and B X640; C-F X770; G X640. 



Lutman found that nuclear division in Closterium takes place at 

 night. This is probably true to a greater or less extent, for most of the 

 Chlorophyceae. 



The division is peculiar. When the cell divides, each of the resulting 

 cells gets a half-cell already of adult size; the other half-cell — the inner 

 one — is very small, but it grows rapidly and, in a day or so, becomes as 

 large as the other half. 



A few of the most common desmids are shown in Figure 47. 



Zygnema. — Zygnema is one of the most common algae of the ponds, 

 swamps, and ditches. The mats are very slippery to the touch. In the 

 field it resembles Spirogyra, but is distinguished by the two character- 



