Ch. VIII, 6] CYCLE OP DEVELOPMENT ' 387 



this process all of the food supphed by the parent plant has 

 been used ; and thenceforth the new plant must depend en- 

 tirely upon its own physiological powers, for the exercise 

 of which, however, it is now fully prepared. 



The successive stages in the developmental cycle of plants, 

 while distinct in principle, largely overlap in practice, so 

 that even before the completion of germination, the young 

 plant has commenced the activities of its next, or seedling, 

 stage. With the spread of its chlorophjdl in hght, it begins 

 to acquire a new food supply of its own, which forms a 

 basis for further development. The root now begins to send 

 out branches, diageotropically guided either horizontally or 

 at definite angles from the vertical main root, though these 

 directions of growth are soon disarranged by obstructions in 

 the soil. Meantime the plumule bud, between the cotyledons, 

 is continuing its development, forming in symmetrical order 

 new leaves, which, at first small and tightly appressed to 

 the stem, later gradualljr open out until they present their 

 full faces to the sun. Simultaneously there is continuous 

 increase in size, and the formation of suitable firm support- 

 ing and other needed tissues. Thus is attained the stage of 



the SEEDLING. 



Gradually the seedling passes into a stage which in case 

 of trees is called the sapling. In the roots new branches 

 spring from the secondary roots, not at definite places or 

 angles, but guided hydrotropically and chemotropicall}^ 

 towards the moistest and richest parts of the soil, where 

 they develop more profuselj^, thus making the root system as 

 asymmetrical as the soil is irregular in texture. Meantime, 

 while the leaves are still in the embryonic stage, new buds 

 develop in their axils, and later, after those leaves have 

 passed their maturity and fallen, grow out into branches 

 which bear new leaves in preciselj' the same manner as does 

 the main stem. These branches, guided diageotropicall}^, 

 grow out at definite angles wth the vertical main trunk, 

 and, possessing also the same symmetrical phyllotactic ar- 



