OF THE ELEMEKTART STRUCTURES. 723 



CHAPTER 1. 



SPECIAL PHYSIOLOGY. 



Section 1. — Physiology of the Elementary Structures 

 OF Plants. 



1. Functions OF Parenchymatous Cells and Parenchyma. 



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

 Plant (^Protococcus nivalis or Palmella cruenta) {figs, 147 and 

 148) merely consist of a single cell, that cell is necessarily 

 capable in such a case, of performing all the actions appertaining 

 to plant life. Parenchymatous 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 special functions 

 observed in cells are, 1. The formation of new cells ; 2. Ab- 

 sorption and transmission of fluids ; 3. Movements in their 

 contents ; and, 4. Elaboration of their fluids, and production of 

 the different materials necessary for development and secretion. 



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

 seen (p, 4), in their earliest conditions, are composed of one or 

 more cells, hence, all the organs which afterwards make their 

 appearance must \)e produced by the modification of such cells, 

 or by the formation of new ones. The formation and growth of 

 cells has already been treated of (see pp. 56—62), and need 

 not be further alluded to. New cells may be either produced 

 by division of the parent cells (p. 58); or by free-ceU formation 

 (p. 56), in the cavities of their parents. 



2. Absorption and Transmission of Fluids. — TheceU-wall of all 

 young and vitally active parenchymatous or prosenchymatous 

 cells is readily permeable by fluids, and we find, accordingly, 

 that liquid matters are constantly being absorbed and trans- 

 mitted through such cells. The power which thus enables cells 

 to absorb and transmit fluids, is called endosmose. This phy- 

 sical force, as will be afterwards shown, is a most important 

 agent in plant-life, for by its agency plants are enabled, not 

 only to absorb crude food by their roots in a fluid state, but 

 also to transfer it upwards, from cell to cell, to the leaves and 

 other external organs, for the purpose of being elaborated by 

 the action of light and air. It is, moreover, by a somewhat 



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