THE VEGETABLE CELL 



283 



portions, distinct from the main portion of the protoplasm, 

 Ifnown BjS plastids. The bulli of the protoplasm, to distinguish 

 it from these specialised portions, is generally called the cyto- 

 plasm. It is not of the same consistency throughout, a 

 generally firmer portion lying next to the cell-wall being known 

 as the ectoplasm. A similar firm layer may frequently be detected 

 round the vacuole. The exact chemical composition of proto- 

 plasm cannot be ascertained, as analysis involves its death, and 



Fig. 614. 



Fie. 615. 



FUj. 614. Cells from leaf of £Zt)dm ; the arrows show tbedlrectiou of the rota- 

 tion of the protoplasm, n. Nucleus, p. Protoplasm or primordial utricle, 



in which are embedded numerous chloroplasts. (x 300.) Fig. 615. 



Two cells from a staminal hair of Ti-adescantia. The arrows indicate the 

 direction of tlie circulation of the protoplasm. )^. Nucleus. ( x 300.) 



this is attended by changes in its substance. It is composed of 

 carbon, hydrogen, oxygen, nitrogen, and probably sulphur and 

 phosphorus. Enclosed in it are always varying quantities of 

 organic substances, such as proteids, fats, carbohydrates, and 

 small portions of various inorganic salts. These various con- 

 stituents are connected with the nutritive processes of the cell, 

 or its metabolism, and hence differ greatly in nature and amount 

 from time to time. 



In the ease of the free-swimming protoplasts with which we 

 began the study of protoplasm, we see that they are in active 

 movement. As the protoplasm becomes enclosed in cell-walls 



