8 



GROWTH 



five millimetres distant from the apex (Figs, i and 2). From this point 

 the rapidity of growth steadily decreases, and ceases at a distance from 



FIG. i. Seedling; of Vicia Faba (nat. size). A marked with lines of Indian ink I mm. apart ; B after 

 6 hours', and C after 24 hours' growth at 23, in moist sawdust behind a glass plate. .5 has increased 

 4-6 mm., C 20 mm. in length. 



the extreme apex of ten millimetres. 



7 a 9 10 Zone 



FIG. 2. Graphic representation of the amount of growth in 

 the zones o to 10 in Fig. I. 2? after 6 hours, C after 24 

 hours. 



It is therefore evident that the 

 elongation of the root is mainly 

 due to the growth in length of 

 the segment-cells just behind 

 the actual apex. The localiza- 

 tion of growth given by this 

 means is never perfectly exact, 

 but is correct in the main if the 

 total amount of growth is not 

 too great, so that the marks do 

 not become too widely separated. 

 This mode of growth applies 

 to all roots, including aerial roots 

 in which the growing zone may 

 attain a length of 30 or even 

 no mm. 1 . The growing zone 



1 Sachs, 1. c., 1874, Bd. I, p. 593 ; Went, Ann. du Jard. Bot. d. Buitenzorg, 1895, T. xn, p. 20. 

 In the slowly growing aerial roots which function as tendrils, the growing zone is no longer 

 than in the case of subterranean roots. It may however be 20 mm. in length in the root-tendrils of 

 Vanilla aromatica. Cf. Ewart, Ann. du Jard. Bot. de Buitenzorg, T. xv, 1898, pp. 234, 237. 



