NATURE OF PLANTS 103 



ness of scion may be modified by the stock. Fruit growers take 

 advantage of this in grafting the cuttings from seedlings that 

 would not bear for several years upon fruiting trees, with the 

 result that the scion comes into fruitfulness the next season. 

 In the same way it is claimed that seedlings may be made to 

 bear earlier than they normally would by grafting them with buds 

 from fruiting trees. 



43. Comparison of Stem and Root. — It will be noticed that the 

 structure of the growing tip of the stem presents several striking 

 departures from that of the root. In the first place a protective 

 structure such as the root cap is not required (Fig. 62). The 

 leaves, and consequently the branches are formed with great 

 regularity from the superficial tissues of the stem, whereas the 

 rootlets are deep seated in origin and irregularly distributed. 

 Furthermore, the elongation of the stem is distributed over 

 several centimeters, while in the root it is confined to a few milli- 

 meters. The leaves and branches are distributed over the entire 

 zone of elongation, while lateral roots do not appear until elonga- 

 tion has ceased. This prolonged growth of the tip of stems is of 

 great advantage in bringing about the proper adjustment of 

 leaves and branches. These organs come into sharp competition 

 with each other as well as with other plants, and so long as growth 

 continues there is a possibility for them to become adjusted to the 

 light without interfering with one another. The mode of elonga- 

 tion of stems and roots is essentially alike. Each has a formative 

 region at the apex characterized by active cell formation and 

 slight elongation, back of this is the zone of rapid elongation dnd 

 following this is the zone in which elongation is gradually ceas- 

 ing and the tissues are assuming their characteristic forms and 

 functions. It is also important to note that the growth of the 

 cells on one side of the stem or root is faster at a certain time 

 than that of the other cells. This will cause the stem to be bent 

 towards the opposite side. This condition of rapid elongation 

 does not. continue on one side for any considerable time but 

 slowly moves from point to point around the stem so that the 

 stem is successively bent from side to side, thus causing the apex 

 to travel in an irregular circle. By these constant movements. 



