P rotococcacece 



219 



by the oblique longitudinal division of the contents of the mother- 

 cell. 



D. bicaudatus A. Br. is a lunate species with the apices greatly prolonged 

 and its chloroplast is destitute of a pyrenoid; length of cells 13 39 p,; diam. 

 of cells 2-55-8 p. ; fig. 91 A. D. dispar W. & G. S. West is unequally 



Fig. 91. A, Dactylococcus bicaudatus A. Br., from near Bradford, W. Yorks. 

 B and C, D. bicaudatus var. subramosus W. & G. S. West, from Widdale Fell, 

 N. Yorks. D, D. dispar W. & G. 8. West, from Dorking, Surrey. (All x 520.) 



developed at the extremities and the cells frequently become irregular; 

 fig. 91 D. The Alga described as D. Debaryanus Reinsch, which often occurs 

 in large numbers as an epiphyte on Cyclops and other small Crustacea, is a 

 species of Characium. 



There is little doubt that D. infusionum Nag. is merely a state in the life- 

 history of Scenedesmus obliquus (Turp.) Kiitz. It is usually aquatic and often 

 occurs in immense quantity in the water of flower-pots and in aquaria. It 

 exhibits great variability of form and its chloroplast commonly contains a 

 pyrenoid ; length of cells 7'5 19 /z, breadth 2'8 5'8 /*. 



Genus Scenedesmus Meyen, 1829. In this genus there is a 

 coenobium of more or less definite form, consisting of a variable 

 number of cells arranged either in a single row or in two alterna- 

 ting rows. The cells are generally disposed in one plane and in 

 some species the terminal cells of the row differ considerably from 

 the. central cells. There is a wide range of variation in the form of 

 the cells, which may be ellipsoid, oblong, or fusiform, and the 

 extremities of all the cells of the coenobium, or of the terminal 

 cells only, may be furnished with one or more spines. In some the 

 cells are longitudinally ridged and in others spines may be 

 attached to the middle region of the cells. There is a large 

 parietal chloroplast, often completely filling the cell, and generally 

 containing a single pyrenoid. Multiplication takes place by the 

 formation of autospores and autocolonies, and rarely by globular 

 resting-spores. In cultures these plants have been said to pass 

 into a palmelloid or gloeocystiform condition. 



