88 



CASSELL'S POPrLAR GARDEmNa. 



known fi'om the radicle in this early stage of growth 

 by its cylindrical form destitute of branches (as a 

 rule) and root-hairs. If, instead of being cylin- 

 drical, it tapers to one end so as to resemble a length- 

 ened cone, the point of the cone is directed up- 

 wards in the reverse dii^ection to that of the root. 

 From its internal structure, absence of root- 

 hairs, and other considerations, it is apparent that 

 this caulicle, which most persons would confound 

 with the root, is really not a root, and has not the 

 office of a root. What the caulicle does is to ujDraise 

 the seed-leaves, or at least the plumule (for the seed- 

 leaves sometimes remain below the surface), to the 



Pig. 15.— Germination of Bean, further advanced than at 

 Fig. 12. The root has peuetrated some distance and 

 given off branches ; the caulicle, still arched, has up- 

 raised the cotyledons and the plumule. 



light and air. Later on it very frequently serves as 

 a reservoir or store for water, or for nutritive sub- 

 stances ; thus, the so-called roots of Tm^nips, Carrots, 

 Radishes, Beet, &c., consist in part, at least, of de- 

 velopments of the caulicle filled with food substances 

 destined for the use of the growing plant. So also it 

 often happens that the root-stock, or " rhizome," is 

 in part, at least, a development of the -caulicle serv- 

 ing as a store-place for food, and indicating to the 

 practical man that the plant possessing it under- 

 goes a period of comparative rest, obtaining its 

 supplies, till growth again begins, from its own 

 resources. As it bursts thi'ough the seed- coats the 

 caulicle has an arched form (Fig. 15), but as its tip 

 becomes liberated from the seed-coat, it straightens 



itself, and by its upward growth thrasts the plumule 

 into the light and air (Fig. 16). 



Movements of the Caulicle. — While growing 

 it worms its way upwards with the same gjTating 

 movement that has been mentioned in the case of 

 the radicle, though the movements in this case are 



Fig. 16.— Seedling Plant of Melon. The primary ro't l"s 

 decayed, but numerous branches have been formed, and 

 the caulicle upraised to bear two leafy cotyledons, aud 

 the first bud or i^lumule. 



less clearly \isible and less distinct, owing to the 

 counteracting influences of the soil, &c. 



3j means of the wiiggiing force exerted by the 

 arching caulicle, the seed-leaves are at length dragged 

 out of the ground, and the tigellum now straightens 

 itself, by additional growth along the concave side, 

 so that the convex side is, as it were, pushed into 

 a straight position by the greater force of growth 

 on the opposite side. Once straight and fi^ee, the 

 cardicle moves more fi^eely (Fig. 17). 



The arching form of the caulicle (a fonn assumed 

 also in many cases by other parts of the plants as 

 they emerge from the soil) tends to protect the young 

 growing point from abrasion, and not only, so, but, 

 as Darwin points out, the arching form, coupl:d 



