ABSORPTION OF NUTEIMENT. 



1. INTRODUCTION. 



Classification of plants with reference to nutrition. — Theory of food-absorption. 



CLASSIFICATION OF PLANTS WITH REFERENCE TO NUTRITION. 



The object of a plant's vital energy, next in importance to the resistance of such 

 influences as are likely to bring about the death of the protoplasm, is growth, i.e. the 

 addition of substance to its body, or, in other words, the absorption of nutriment. 

 A living plant, whether consisting of a single cell or of a vast community of cells, 

 takes up food from its environment in quantities varying according to the needs of 

 the moment. But its method of action — how it sets about acquiring possession of 

 this raw material, how it manages to incorporate the substances absorbed from with- 

 out, how it contrives to retain only such part as is useful to it, and to reject and get 

 rid of, like ballast, what does not subserve its own growth — is infinitely varied. 

 This variety in the processes of food-absorption corresponds, on the one hand, to 

 differences in the habitat of plants, and, on the other, to the requirements of particu- 

 lar species, which requirements in their turn depend upon a specific constitution of 

 the protoplasm in each species concerned. The difference must be very great 

 between this process as manifested in plants which are immersed in water during 

 their whole lives and the same as it occurs in plants which live in desert sands and 

 are not supplied with water for months together. And again, absorption in those 

 fungi which grow luxuriantly on damp timber in the deep obscurity of a mine must 

 take place very differently from the corresponding process in the delicate alpine 

 plants which on our mountain slopes are exposed periodically to the most intense 

 sunlight, and then, for weeks at a time, are wreathed in sombre mists. So, also, 

 the reciprocal action between plants and their environment must have a character of 

 its own in the case of parasitic growths which absorb their food fi-om other living 

 organisms, and in those remarkable plants, too, which catch and devour small insects, 

 and in such minute organisms as yeast, the vinegar ferment, and others, which play 

 so important a part in our daily life, and lastly, in the gigantic trees which form our 

 forests. 



To acquire a general notion of these forms, with reference to their varieties as 

 regards nutrition, it is best to classify them in the first place in groups according to 

 their habitat, viz.: into water-plants or hydrophytes, stone-plants or lithophytes, 

 land-plants, and epiphytes. But here again it is necessary to remark that no sharp 



