General Physiology of the Plant. 1 97 



III. in this relation). Under the head of anabolism we will 

 discuss the absorption and assimilation of food-stuffs, both 

 of which processes may be summed up under the one term 

 nutrition. We will also consider the circulation of the 

 various food-stuffs, both in their prepared and unprepared 

 states, through the plant-body, and the storage of the excess. 

 Under the head of katabolism, on the other hand, we will 

 discuss the breaking down of protoplasm, and the formation 

 in consequence of degradation products, or katastates, 

 which may be again subdivided into secretions, or kata- 

 states still useful in the plant economy, and excretions, or 

 katastates which must be got rid of. Lastly we will deal with 

 the results of katabolisn?, or the various ways in which the 

 energy liberated by the decomposition of protoplasm mani- 

 fests itself in the plant These results will be found to group 

 themselves under the following headings : first, growth and 

 movement ; secondly, irritability or sensitivity ; thirdly, 

 heat, light, and electricity ; and lastly, phenomena con- 

 nected with the formation of reproductive cells. 



I. Anabolism. 



A. Nutrition. All the food of the plant must necessa- 

 rily be absorbed in the fluid form, i.e. in the form of a liquid 

 or a gas. Solids absorbed are taken up in solution in water, 

 those which are naturally insoluble in water being made so 

 by some substance (acid) produced by the plant. 



We must first consider the laws which govern the 

 absorption of liquids and gases. All food material must 

 pass through the cell-walls of the leaf and root-hairs, which, 

 we have already seen, are the organs of absorption. Let us 

 examine first the passage of liquids, i.e. water with salts in 

 solution, through the cell-walls of the root-hairs ; and it may 

 be well to illustrate this subject by a simple physical experi- 

 ment, before taking up the special case before us. 



A glass vessel is taken containing distilled water, and in 

 it is suspended a smalle/ glass vessel, which, however, has a 



