LECTURE IL 



THE TYPICAL ROOTS OF VASCULAR PLANTS. 



Lr has been already remarked in the first lecture, while considering the 

 differences between roots and shoots, that the primary and essential character of 

 the root consists in that it becomes, first of all, developed as an organ of attachment 

 on or in a substratum, and, when the latter is the case, it is at the same lime the 

 medium of absorption of nutritive matters contained in the substratum. Since, 

 moreover, assimilation — i. e. the production of organic vegetable substance — is foreign 

 to its physiological purpose, the instrument of assimilation, chlorophyll, is also 

 wanting to it : though it is not thereby precluded that in certain rare cases, when 

 the roots are developed in air or water and thus exposed to light, chlorophyll may 

 also arise in them. However I shall return to the physiological properties of roots 

 afterwards. INIeanwhile, it will be to the purpose to consider the relations of 

 organisation ; and we will concern ourselves, according to the scheme of comparative 

 organography given above, first with the typical, and then with the rudimentary 

 and reduced forms of roots. 



We find typical, and at the same time very highly organised roots, in the 

 large majority of vascular })lants, the phanerogams and higher cryptogams : 

 botanists for about the last forty years have accustomed themselves to term these 

 organs exclusively roots, which is from a purely formal point of \iew but half 

 justifiable, and from the standpoint of physiological organography must be entirely 

 rejected. 



In vascular plants with upright main stems, as the Sunflower, Tobacco, Hemp, 

 and others, we meet with a root-system developed comjjletely in the earth, and 

 composed of long, cylindrical fibres of varying thickness, which is in ordinary 

 language simply termed the root; in scientific language it is however more to the 

 purpose to call each one of these fibres a root. In many cases the first root, 

 already present in the embryo of the plant, becomes vigorously developed, pene- 

 trating perpendicularly into the earth [w, Fig. 4) : from it spring, radiating 

 laterally in two, three, or more directions, numerous new roots {n) which grow 

 horizontally or obliquely downwards, and in their turn again produce new root-fibres, 

 and in such a way that the new, young roots always arise behind the growing 

 end of what is the mother-root for the time being. In the case here considered, 

 which is realised especially in trees and annual erect plants, the whole root-system 



