34 PATTERNS AND PROBLEMS OF DEVELOPMENT 



hibit or greatly retard development beyond a very early stage of bud pri- 

 mordia below it or may determine their development as lateral branches. 

 When this tip is removed or inhibited, the usual result is that the upper- 

 most buds develop, or one or more of the uppermost branches reconstitute 

 a main stem and development or transformation of axes below is in- 

 hibited. On removal of the reconstituted axis or axes the next uppermost 

 buds or branches react first, and so on. Even in the potato tuber, which 

 is a modified subterranean stem, this relation appears to some extent 

 (Appleman, 1918, 1924). In certain other plants only a difference in rate 

 or time of development of buds along the stem results from removal of the 

 tip, the uppermost buds developing first, and others in basipetal order. 

 The relation of development of lateral roots to a main root tip is very sim- 

 ilar. 



Adventitious buds which develop from differentiated cells in some 

 plants after removal of all growing tips and preformed buds may also 

 show preferential localization or more rapid development at more apical 

 levels. When they develop on pieces of roots, as in the dandelion (Nemec, 

 1908), they tend to be localized at the basal end of the piece, that is, on the 

 end toward the stem; but in very short pieces they may appear anywhere 

 without preferential localization. The data indicate a gradient pattern 

 more or less effective in determining localization of the buds in longer 

 pieces but ineffective in very short pieces because in them there is so little 

 regional difference. Rhizoids and roots usually show an opposite localiza- 

 tion differential from shoot buds, that is, they tend to appear basally on 

 isolated stem pieces; they can, however, be determined at any level. 



The art of pruning, trimming, and "forcing" development of certain 

 axes by removal of others in plants depends on reconstitution by substitu- 

 tion and on presence of a gradient pattern of some kind along the axes con- 

 cerned. 



RECONSTITUTION IN ANIMALS IN RELATION TO BODY-LEVEL 

 CILIATE PROTOZOA 



Some indications of a longitudinal gradient appear in connection with 

 fission in ciliates (p. 24); and, although experiments on reconstitution 

 have usually been chiefly concerned with other problems, they add some 

 evidence. Reconstitution of the gullet of Bursaria after section progresses 

 from the anterior end, as in fission (Lund, 191 7). The multiple monsters 

 which sometimes result from incisions in the cell body of Paramecium may 

 show a considerable number of partial axes, each of which represents at 



