LECT. VIII.] STRUCTURE OF HERBACEOUS ROOTS. 443 



knobs. It appears to me, that when an herba- 

 ceous plant is partially stinted of moisture and 

 nutriment in the soil, the functions of some of the 

 rootlets are destroyed, owing to the sap vessels 

 losing their irritability and becoming obstructed; 

 while at the same time the absorbing orifices of the 

 cuticle become also impermeable. But as the other 

 rootlets still continue in a natural state, the plant 

 is kept alive; and as the proper juices are se- 

 creted, the usual supply is sent to the affected 

 rootlets, which, however, not being able to assi- 

 milate it, the cellular matter in which it is depo- 

 sited swells, and the rootlets assume the cha- 

 racter of the knobs in question *. 



From the examination of the structure of her- 

 baceous roots, which we have just concluded, se- 

 veral practical hints may be obtained. Thus it ap- 

 pears probable, that those roots, containing bland 

 saccharine or amylaceous secretions, which possess 

 a moist cellular central part, are the best adapted 

 for rewarding the skill of the horticulturist, in 

 converting them into articles of food for man and 

 other animals. We also discover the reason that 



* Mr. Keith says, " This anomaly seems to be merely the 

 " result of a provision of Nature, by which the plant is en- 

 " dowed with the capacity of collecting a supply of moisture 

 " suited to existing circumstances, and hence of adapting itself 

 to the soil in which it grows." Syst. of Phys. Bot. vol. ii. 

 p. 271. 



