220 NUTRITIVE METABOLISM 



and other arrangements with these are but of secondary impor- 

 tance (granular theory of Altmann). 1 



A denser globose body, generally with a definite limiting mem- 

 brane, lies imbedded in the cytoplasm constituting the nucleus. 

 The essential part of this organ appears to consist of an irregular 

 branching network composed of linin, a granular substance 

 resembling extra-nuclear protoplasm in its chemical composition 

 and granular appearance, and chromatin a deeply staining sub- 

 stance, which often appears as masses or granules imbedded in 

 the limn or may be separated in a single mass constituting the 

 nucleolus. In addition a clear substance occupies the interspaces 

 of the network. Numbers of granular bodies of definite shape 

 termed plastids are also to be found at various points in the cell. 

 The protoplasm immediately surrounding the nucleus appears to 

 be denser, and less differentiated morphologically, than the outer 

 portions of the mass, and these two regions may be denoted as 

 the endoplasm and ectoplasm respectively. Large spaces, con- 

 taining clear solutions or various substances, appear in the plasma 

 and are termed vacuoles. The ectoplasm is limited by a distinct 

 membrane, and lies against the outer wall which makes up such 

 a large share of the visible portions of plants. The wall may 

 show the most diverse forms and thicknesses and is generally re- 

 garded as a secretion product of the living substance, and many 

 changes may be induced in it at all stages of its existence both as 

 to structure and composition. 



289. Chemical Properties of the Cell. The nucleus and cyto- 

 plasm have some constituents in common, but the former is char- 

 acterized by the fact that it is chiefly composed of nucleins and 

 nucleo-proteids in addition to the nucleo-albumins, globulins, 

 albumins and peptones of which cytoplasm is largely made up. 

 Chromatin is composed almost wholly of a compound of nucleinic 

 acid (C^H^Nj^Ojy) and certain proteids, while the linin is com- 

 posed of proteids readily soluble in acid pepsin. The proteids 

 of the cytoplasm show the more diverse characteristics and the 



1 Wilson, E. B. The cell in development and inheritance, p. 17. 1900. 



