I04 INDIVIDUALITY IN ORGANISMS 



the development of parts apical to the original level of 

 the piece takes place only in relation to the development 

 of a new apical end, while the development of parts basal 

 to the original level of the piece is determined by the 

 piece itself, even in the absence of a head. All the facts 

 indicate that the same relation exists in other animals. 

 It has already been pointed out (pp. 83-86) that 

 when new growing tips arise in wound callus or from 

 differentiated cells of plants, growth and differentiation 

 proceed from these, not toward them. Plant stems, 

 lateral branches, and leaves are subordinate parts or 

 individuals of the plant and develop only under the 

 dominance of growing tips. The root of the higher 

 plant is likewise a subordinate individual. It possesses 

 a growing tip and between this growing tip and other 

 parts of the root individual the same relations of domi- 

 nance and subordination exist as between the stem-tip 

 and other levels of the stem, but the root as a whole 

 develops only in subordination to some part of the plant, 

 a stem-tip, a stem, a branch, a bud, a leaf, or some part 

 of a root system already present. The same is true for 

 the root-like structures, the rhizoids of the lower plants. 

 The roots and rhizoids of the plant have apparently 

 much the same relation to the organism as a whole as 

 do the stolons of Tubularia and related forms. They 

 are individuals, each with an axial gradient and a 

 dominant region of their own, but they are specialized 

 individuals, and arise from the basal region of the 

 major axis of the individual which controls their forma- 

 tion, whether it is a single bud or branch, a leaf, or the 

 whole stem of a composite plant individual. It is prob- 

 able that these subordinate individuals really represent 



