154 INDIVIDUALITY IN ORGANISMS 



so-called '' adventitious" buds, which may arise from 

 differentiated cells, as in the case of the begonia (Figs. 

 38, 39), and may be scattered irregularly over various 

 parts of the plant according to the conditions of the 

 experiment. Often the presence of a single one of the 

 original buds is sufficient to inhibit the formation of 

 these adventitious buds. The appearance of adventi- 

 tious buds on plants in nature is usually due to the 

 weakening of existing growing tips through advancing 

 age or injury of some sort. 



Such adventitious buds very often arise in large 

 numbers simultaneously without any regular arrange- 

 ment with reference to each other. The absence of 

 definite space relations in such cases is undoubtedly 

 due to the fact that they arise simultaneously, or nearly 

 so. Various cells here and there which happen to have 

 a slightly higher metabolic rate than others begin to 

 develop into new buds at about the same time; conse- 

 quently none of the buds is dominant over the others. 

 If, however, one of the adventitious buds gets a start 

 beyond the others in any way, it inhibits the further 

 development and may even bring about the death of 

 others within a certain distance of it. Moreover, where 

 a gradient is present in the part on which the buds ap- 

 pear, so that one or more buds appear first in a certain 

 region — the region of highest metabolic rate in the part — 

 they inhibit the growth of others within a certain dis- 

 tance or throughout the part. 



In various conifers the dominance of the growing tip 

 of the main stem appears in a somewhat different form. 

 In these trees, as long as the growing tip of the main 

 stem is present and active, lateral branches arise radially 



