THE ALGAE 6i 



Haematococcus nivalis is closely similar to the type we have described. 

 The resting cells contain an abundance of red pigment and, since the Alga 

 is found on the snow in Alpine and Arctic regions, it gives the appearance 

 of blood-red patches, from which it has gained the name of the " red-snow " 

 plant. It also sometimes comes down in great quantities in rain, thus giving 

 rise to stories about " rains of blood." 



Reproduction 



Reproduction is usually carried out by simple longitudinal division of the 

 motile cell, no zoospores being formed. The contents of a cyst may some- 

 times divide to form an extensive palmella stage, and it is from such resting 

 cells that the gametes are formed. They are minute motile swarmers, with 

 no cell wall, but otherwise like the normal cell. 



Turning now from the unicellular types to the colonial ones, we find 

 various examples consisting of a number of chlamydomonas-like cells 

 embedded in mucilage. The size of these colonies varies according to the 

 number of cells concerned. Both in shape and in the number of component 

 cells each species is quite distinct and constant. We shall consider here 

 four examples, Goniiim, Paudorina, Eudorina and Volvox. 



Gonium 



This is the simplest of the colonial Volvocales. The colony or coenobium 

 consists of a sixteen-celled plate (Fig. 36), which is square in surface view 



IPP V ^ 



A B 



Fig. 36. — Gonium sp. A, Surface view of a mature colony. B, Colony in 

 side view showing the curvature. 



but thin and slightly curved in side view. It is made up of four central and 

 twelve peripheral cells, each having the chlamydomonad structure. The 

 cells are connected by slight protrusions so that triangular spaces are formed 

 between them, while the centre is made up of a squarish area of mucus. The 



