

METABOLISM OF GREEN PLANTS 31 



tion the so-called DORMANT FORM which may be assumed when 

 the water in which it has been living dries up. In this 

 condition the organism consists of a spherical mass of pro- 

 toplasm near the center of which is a rather large nucleus. 

 The protoplasm, which appears greenish or reddish for rea- 

 sons to ; be discussed later, is enclosed within a distinct, rigid 

 cell wall. This has been secreted by the cell and is com- 

 posed of CELLULOSE, a carbohydrate which is especially 

 characteristic of plant cells. It is evident that the organism 

 is a single cell. (Fig. 9.) 



Sphaerella in this phase is able to withstand unfavorable 

 conditions for several years at least. All the life processes 

 of the protoplasm are reduced to the lowest ebb; so low that 

 it is difficult to demonstrate any chemical change whatsoever 

 going on. Life in a dormant condition is not peculiar to 

 Sphaerella, but is quite a characteristic phase in the life of 

 many animals and plants, being most familiar to us in the case 

 of plant seeds, some of which are known to retain their vital- 

 ity for nearly a century under proper conditions. 



When dormant specimens of Sphaerella are placed in rain 

 water in the sunlight active life shortly is resumed. The cell 

 wall swells up and the protoplasm within divides twice, with 

 the result that four smaller but otherwise essentially similar 

 cells, known as SPORES, take the place of the original cell and 

 are set free by the rupture of its wall. The four daughter 

 cells soon become more or less oval in outline and secrete 

 cellulose walls of their own. The cell walls do not fit closely 

 about the body of protoplasm, termed the PROTOPLAST, but 

 are separated from it by a liquid-filled space, or vacuole, 

 except where cytoplasmic strands extend through the vacuole 

 to the wall. But a more remarkable change occurs at the 

 same time two long slender cytoplasmic strands are 

 developed from the more pointed end of the cell, and these, 



