36 PROTOZOA 



the word. In this sense, ves^etal nutrition is the utilisation of 

 nitrogenous substances that are more simple than proteids or 

 peptones, together with suitable organic carbon compounds, etc., 

 to build up proteids and protoplasm. The simplest of organisms 

 with a vegetal nutrition are the Schizomycetes, often spoken of 

 loosely as "bacteria" or " microbes," in which the differentiation of 

 cytoplasm and nucleus is not clearly recognisable. Some of these 

 can build up their proteids from the free uncombined nitrogen of 

 the atmosphere, carbon dioxide, and inorganic salts, such as 

 sulphates and phosphates. But the majority of vegetal feeders 

 require the nitrogen to be combined at least in the form of a 

 nitrate or an ammonium salt — nay, for growth in the dark, they 

 require the carbon also to be present in some organic combination, 

 such as a tartrate, a carbohydrate, etc. Acetates and oxalates, 

 " aromatic " compounds ^ and nitriles are rarely capable of being 

 utilised, and indeed are often prejudicial to life. In many 

 vegetal feeders certain portions of the protoplasm are specialised, 

 and have the power of forming a green, yellow, or brown pig- 

 ment ; these are called " plastids " or " chromatophores." They 

 multiply by constriction within the cell, displaying thereby 

 a certain independent individuality. These plastids have in 

 presence of light the extraordinary power of deoxidising carbon 

 dioxide and water to form carbohydrates (or fats, etc.) and 

 free oxygen ; and from these carbohydrates or fats, together with 

 ammonium salts or nitrates, etc., the vegetal protoplasm at large 

 can build up all necessary food matter. So that in presence of 

 light of the right quality ^ and adequate intensity, such coloured 

 vegetal beings have the capacity for building up their bodies 

 and reserves from purely inorganic materials. Coloured vegetal 

 nutrition, then, is a process involving the absorption of energy ; 

 the source from which this is derived in the bacteria being very 

 obscure at present. Nutrition by means of coloured plastids is 



' Whence the antiseptic powers of such aromatic alcohols as phenol and thymol, 

 and acids as salicylic acid, etc., and their salts and esters. 



'^ The portion of the spectrum that is operative in " holophytio " nutrition is the 

 red or less refrangible half, and notably those rays in the true red, which are absorbed 

 by the green pigment chlorophyll, and so give a dark band in the red of its 

 absorption spectrum. The more refrangible half of the spectrum, so active on 

 silver salts, that it is usually said to consist of "chemical rays," is not only 

 inoperative, but has a destructive action on the pigments themselves, and even 

 on the protoplasm. Chlorophyll is present in all eases even when more or less 

 modified or masked by the accompaniment of other pigments. 



