76 



INDIVIDUALITY IN ORGANISMS 



growing tip consists of several or many cells. Figs. 21 

 and 22, longitudinal sections through the growing tips of 

 a stem and a root respectively, show the gradients in cell 



Figs. 21, 22. — Axial developmental gradients in growing tips of 

 seed plants: Fig. 21, stem-tip of Hippuris; Fig. 22, root-tip of Trades- 

 cantia (from preparations loaned by Department of Botany, University 

 of Chicago). 



size and protoplasmic condition which extend from the 

 growing tips. In the stem-tip these gradients extend to 

 a much greater distance than in the root- tip and Fig. 21 

 shows only a fraction of them. 



