Cholorophycae - Volvocales - Haematococcus (Sphaerella)

Phylum Thallophyta - The Algae - Cholorophycae - Volvocales - Haematococcus (Sphaerella) 

The active cell in this organism differs from that of Chlamydomonas chiefly in the separation of the protoplast from the cell wall. The cell wall itself is well defined but thin and is composed of cellulose. It is separated from the cytoplasm by a thick mucilaginous inner wall which is penetrated by fine protoplasmic threads. Embedded in the central cytoplasm is a large hemispherical chloroplast which is hollowed out and resembles that in Chlamydomonas. In fact the structure of the whole protoplast is sub­stantially similar to that of Chlamydomonas, except that there are numerous contractile vacuoles and seyeral pyrenoids. 

Haematococcus obtains its name from the fact that the cell is often red in color. This is due to the presence of a carotinoid red pigment, haeatochrome, which masks the green color of the chlorphyll. The actual color of any particular cell depends upon the relative proportion of haematochrome present, which in turn depends on the supply of nitrogen compounds. The Alga very readily forms cysts by the withdrawal of the flagella and the rounding up of the cell, in fact it is in this condition that the organism is generally seen. 

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 in Sphaerella

Reproduction is usually carried out by simple longitudinal division of the motile cell, no zoospores being formed. The contents of a cyst may some­times divide to form an extensive palrnella stage, and it is from such resting cells that the gametes are formed. They are minute motile swarmers, with no cell wall, but othe'rwise 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. 

Posted in Botany