NATURE OF PLANTS 97 



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. There are several remarkable cases of graft- 

 ing where the scion underwent variations very suggestive of those 

 seen in the offspring resulting from crossing two different plants. 

 For example, a white sugar beet was grafted upon the ordinary 

 red beet. The scion was apparently unaffected but the seed 

 from it produced the next year 71 per cent white beets, 28 per 

 cent reddish beets and .6 per cent red beets. 



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 millimeters. 

 The leaves and branches are distributed over the entire zone of 

 elongation, while lateral roots do not appear until elongation 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 elongation 

 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 and 

 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 



