401 THE STRUCTURE OF ECONOMIC PLANTS 



the region just beneath form the regenerated part, root or shoot." 

 Crooks (7), in a detailed study, found specific differences in the 

 ontogeny of adventitious roots and adventitious shoots. 



Adventitious Buds. — When the growing points of young 

 plants are injured or removed, the axis readily produces shoots; 

 and when the injury occurs above the cotyledonary node, an 

 axillary bud becomes active and produces a shoot. In his experi- 

 mental work. Crooks removed all the organized buds by severing 

 seedlings of various ages at different levels below the cotyledonary 

 node, and in all plants which were not more than ten days old, from 

 twenty to fifty adventitious buds developed on the remaining lower 

 portion of each hypocotyl. This occurred even when the top of the 

 plant had been removed to within a few millimeters of the ground 

 level. In cases where plants two months old were similarly 

 treated, approximately 60 per cent died without forming buds. 



In seedlings less than ten days old, the origin of adventitious buds 

 continues for six to eight days after the severing of the axis; and, 

 since they are not all initiated at the same time, the hypocotyl 

 may at one time have some adventitious buds which are large 

 enough to show small leaves while others are in earlier stages of 

 development. By the time that eight to ten of the buds have 

 differentiated leaves, one of them usually outgrows the others. 

 There is no spatial relationship of the dominant bud to any of the 

 others, or to any special point on the hypocotyl, nor is the more 

 rapidly growing bud necessarily the first one to be formed. Occa- 

 sionally, more than one bud may continue development. The 

 shoot which is formed by the growth of the adventitious bud 

 develops an unbranched axis until the formation of the inflores- 

 cence; and it matures at about the same time as do plants of the 

 same age which are uncut, but it attains only about one-half their 

 height. 



In the ontogeny of the adventitious bud, the first evidence of 

 differentiation, following the abscission of the upper portion of the 

 hypocotyl, is the formation of large intercellular spaces, resembling 

 those of the mesophyll, in the cortical parenchyma of the hypo- 

 cotyl. This occurs at the point of bud origin, and the bud is then 

 initiated by the divison of a single epidermal cell, quickly fol- 

 lowed by a second division so that a four-celled primordium is 

 formed. (Fig. xo4. A, 5.) Five or six of the epidermal cells 

 adjoining the derivatives of the first meristematic epidermal cell 



