472 



On the Structure of Roots. 



The peculiarities of this kind of root are well seen in onions 

 raised from seed ; the bulb is really the base of the stem enclosed 

 in leaf-scales, and this bears on its under surface a circle of 

 thread-like adventitious roots, which do not arise from the 

 centre of the base of the stem, but at its sides or eds;es. But 

 exactly similar adventitious roots are found in abundance of 

 Dicotyledons which are propasfated by offsets, tubers, runners, 

 &c., of which the strawberry, the creeping^ crow-foot, &c., are 

 common examples. Roots of a fibrous character are, however, 

 met with as productions of a true descending axis in many Dico- 

 tyledonous plants, more particularly annuals. This condition arises 

 from the main axis of the root throwing out numerous long 

 branches which repeat the ramification (fig. 4). These branches 



arise from the sides of the tap- 

 root in very regular order irj many 

 plants, standing in two, four, or 

 five equidistant rows, which are 

 naturally perpendicular, but by a 

 twisting of the tap-root are some - 

 times rendered oblique. But 

 their arrangement does not always 

 exliibit tlie spiral character wliich 

 we see in the arrangement of 

 leaves, and which is generally 

 very evident in the arrangement 

 of the adventitious roots at the 

 base of Monocotyledonous stems. 

 The finer branches of the roots 

 of Dicotvledons and Monocotyle- 

 dons, but more particularly of the 

 former, are clothed more or less 

 al)undantly with fine hair -like 



Moot, of a young plantof Groundsel, with adyen- flhj-ils, of which more will be 



said hereafter. These must not 

 be confounded with the real root- 

 lets. Roots of both the kinds above distinguished exliibit a 

 great variety of external forms and modifications of internal struc- 

 ture. Tliese are connected in part, especially the former, with 

 the "habit," or mode of life, of the particular plants, and it will 

 be desirable to direct attention to some of the more striking and 

 instructive instances, before entering upon the special examination 

 of the roots especially interesting to the farmer. 



While we observe a remarkable simplicity in the organization 

 of plants, as regards the number of physiologically different kinds 

 of parts of which they are composed, even a limited acquaintance 

 with vegetable life teaches us, that the simplicity of general plan 



titiiius roots arising from the lower part of the 

 stem, above the tap-root. 



