10 ELEMENTARY STUDIES IN BOTANY 



by the protoplast, and which forms a delicate but tough and 

 elastic layer. 



The protoplast within its cell-wall is a very complex 

 structure, which does a great variety of work. There are 

 always at least two distinct regions or organs of the pro- 

 toplast, which differ in appearance and in work. The 

 ^\ nucleus is usually a globular mass of protoplasm (Fig. 1), 

 lying in the midst of the protoplast, and marked off sharply 

 by a delicate investing membrane. It is impossible to 

 tell all that the nucleus does, but it is conspicuous in the 

 work of cell-division, that is, the process by which a cell 

 divides and forms two new cells. 



The remainder of the body of the protoplast, in which 

 ^ the nucleus lies imbedded, is called the cytoplasm. -It" must 

 not be thought that the cytoplasm is just a mass of pro- 

 toplasm around the nucleus, for it has a structure of its 

 own, and is especially conspicuous in the general processes 

 of nutrition, which means the chemical and physical 

 processes that take place in connection with the use of food. 



In green plants, such as the Algae, there is a third organ 

 C of the protoplast, called the chloroplast (Fig. 1). Chloro- 

 plasts are protoplasmic bodies of various forms among the 

 Algae, but among the higher plants they are usually more 

 or less globular. There may be a single chloroplast in a cell 

 or there may be several chloroplasts, and they are dis- 

 tinguished from the nucleus or from any other body in the 

 cell by their green color, a color due to the presence of 

 a green stain called chlorophyll. The peculiar work of the 

 chloroplasts is to manufacture food from raw material, 

 the details of which are outlined in the next chapter. 



A very important fact to know in reference to the cell 

 is that the pj*otoplast is saturated with water when active. 

 The water accumulates in the protoplasm, until the cell 

 swells and the wall becomes stretched and tense. This 

 swollen condition of the cell is called turgor, and it is one 



