OF THE ELEiIE>-TA2T STUrCXrRES. 729 



CH-IPTEE 1. 



SPECIAL PHYSIOLOGY. 



Section 1. — Physiology of the Elementary Steucttees 

 OF Plan'ts. 



1. FUNCTIOXS OF PAEEXCHYMATOrS CeLLS AXD PaEEXCHYJIA. 



— As the simplest forms of Vegetable life, such as the Eed Snow 

 Plant (Protococcus nivalis or Palmella cruenta) {figs. 1 and 2), 

 consist of a single cell, such a cell is necessarily capable of per- 

 forming all the actions appertaining to plant life. Parenchy- 

 matous tissue also constitutes the whole structure of Thallogens, 

 as well as the soft portions of all plants above them ; hence the 

 physiology of parenchymatous cells is of the first importance. 

 The more important vital actions of cells are, 1. The formation of 

 new cells ; 2. Absorption and transmission of fluids ; 3. Move- 

 ments in their contents ; and, 4. Elaboration of their fluid con- 

 tents, and production of the different materials necessary for 

 development and secretion. 



1. The Formation of Xeiu Cells. — All plants, as we have seen 

 (p. 6), in their earliest conditions, are composed of one or more 

 cells, hence all the organs which afterwards make their appear- 

 ance must be produced by the modification of such cells, or by 

 the formation of new ones. 



The subject of cell-formation or cytogcnesis has engaged the 

 attention of many able physiologists, by whose united labours 

 we have now arrived at tolerably definite conclusions upon the 

 main points of the inquiry ; and although many of the subordinate 

 ones are still involved in obscurity, yet the processes are better 

 understood than the corresponding ones in animal tissues. Our 

 limits will not allow of describing in detail all the theories of 

 cell-formation which have been from time to time brought forward 

 by different observers ; neither is such necessary, since all are 

 now agreed upon the essential principles of the process : we shall 

 therefore confine ourselves to a general outline of the subject. 



Cells can only be formed from that thickened fluid called 

 protoj)lasm which is contained in their interior, or has been ela- 

 borated by their agency ; hence cells can in no case be formed 

 without the influence of living organisms. The nature of proto- 

 plasm has been already fully described. By various observers 

 the formative matter of cells has been called organisable matter ^ 



