146 CONSERVATIVE ORGANS. [LECT. IV. 



the young plant which is the seminal production 

 of the same parent. Whilst the sucker is attached 

 to the root on which it is formed, it derives its 

 nourishment through the same organs that supply 

 the principal stem, which, consequently, must 

 become impoverished in proportion to the number 

 of suckers that surround it. 



3. The KNOB or TUBER (Tuber) is a solid fleshy 

 body, attached to many fibrous-rooted plants, 

 either immediately at the basis of the stem under 

 the rootlets, or mediately by means of cords or 

 wires which proceed from the basis of the stem. 

 The tuber itself is not furnished with any rootlets 

 or fibrils ; which circumstance distinguishes it from 

 nodular and globular roots, with which it is fre- 

 quently confounded in the description of plants. It 

 is composed of cellular substance filled with a moist, 

 amylaceous fecula; is covered with a cutis vera 

 and epidermis ; and furnished with vessels, which 

 are collected at one point or at different points on 

 the surface, where a bud or gem and rootlets are 

 protruded when the tuber, has attained its full ma- 

 turity, and is placed in a situation favourable to 

 vegetation*. It is, in fact, a reservoir of nutriment 



* Mirbel thus describes tubers : " Les tubercules, qui ont 

 " fait dormer le nora de tubereuse a certaines racines, sont des 

 " renflemens charnus, souvent arrondis, masses de tissu cellulaire, 

 " que parcourent quelques vaisseaux qui se rendent vers tous les 

 " points de la surface, d'ou doivent partir les filets radicaux et 

 " les turions. Les poches du tissu cellulaire des tubercles sont 



