LECTURE III. 



ROOTS {continiuir^f. 



METAIMORPHOSED AND REDUCED ROOTS OF THE VASCULAR 

 CRYPTOGAMS; RUDIMENTARY ROOTS OF THE MOSSES AND 

 THALLOPHYTES. 



In the last lecture, I kept in view only the typical forms of roots of the 

 vascular plants, and their most important peculiarities. According to the mode of 

 life of the plants concerned, however, more or less extensive deviations from the 

 typical form of root may appear even in vascular plants. These deviations are to be 

 distributed chiefly in three categories ; thus, we have in the first place roots which, 

 originally quite typical, only modify their form .and properties at a later period 

 of life, in order to serve special objects for the plant ; then are to be noticed 

 the aerial and aquatic roots which, from the first, undertake a function more or 

 less departing from the normal, and possess accordingly an abnormal organi- 

 zation ; thirdly, we find in parasites among vascular plants a continuous series 

 of degenerations, through which their roots, in consequence of more and more 

 pronounced parasitism, finally lose all the anatomical peculiarities of typical roots, 

 though the most important physiological properties remain preserved to them. 

 And finally we shall consider, in addition to these metamorphoses, the roots of 

 Mosses, Algae, and Fungi, especially pointing out that the so-called rhizoids of 

 these plants are in fact nothing more than simply organised roots, different, it 

 is true, in their anatomical structure from those of vascular plants, but agreeing 

 with them completely in physiological relations. 



The first category named above comprehends the lignified older roots of 

 Conifers and other trees, the soft, perennial, turnip-shaped roots of many vegetables, 

 true subterranean root-tubers, as well as some aerial roots. They have all 

 the common pecuHarity of being, fundamentally, typical roots, which eventually 

 acquire other properties. This is perceived most plainly in perennial woody 

 roots. The tap-root of the seedling of a tree with its first ramifications is, in 

 the beginning, thoroughly typical, even with reference to those peculiarities which 

 stamp it as a nutritive organ. When, however, the young tree becomes larger, 

 it requires a firmer hold in the ground, and the roots become thicker and more 



