54 PLANT-LIFE 



In the asexual mode the flagella are first drawn into 

 the body; then the protoplast divides into two masses. 

 Each of these masses may secrete a cell-wall and pro- 

 duce flagella, or, more frequently, each mass divides 

 into two, so that four daughter-cells are produced within 

 the wall of the parent cell. All four cells become per- 

 fect individuals, escape from the membrane enclosing 

 them, and enter upon an active life. There are several 

 species of Chlamydomonas, and it seems that in nearly 

 all sexual reproduction is due to the conjugation of equal 

 gametes, which fuse to form a zygote, the latter giving 

 rise to several individuals. But in one species large and 

 small gametes are produced, indicating differentiation 

 of sex. 



Chlamydomonas, then, represents a distinct advance 

 in the evolution of plant forms. In Euglena we saw a 

 suggestion of an organism adopting plant characters, but 

 we noted the absence of cellulose, and we discovered 

 no evidence of sex. In Chlamydomonas a cellulose wall 

 appears, nutrition is wholly plant-like, and reproduction 

 is both asexual and sexual. 



The so-called " Ked-snow," which occurs on Alpine 

 snowfields in bright crimson patches, is due to vast 

 numbers of a Chlamydomonas-like Alga, which has been 

 variously named Sphcerella nivalis, Hcenrntococcus flu- 

 vialis, and Chlamydomonas nivalis. The red colour is 

 due to a pigment — hsematochrome — which masks the 

 green chlorophyll of the cell. The pigment may be a 

 species of light filter, allowing only such rays to pass as 

 will be useful in maintaining the vitality of the Alga 

 in its exposed situation. While the snow upon which 

 the tiny plants lie is frozen the cells are not motile, but 



