340 LECTURE XV. 



than in stems, so that the growing region is altogether 

 shorter. 



The measurements were made upon a primary root of Vicia Faba : 

 in this case the lengths were only of i mm., and the time 24 hours. 



Increment. \ Increment. 



i '3 mm. 

 ... 0-5 

 0-3 



0*2 

 O'l 



In this case the length of ti\z punctum vegetationis was not 

 more than I millimetre, and that of the second region not 

 more than 9 millimetres. 



There is, however, no abrupt transition from the one region 

 to the other. If we imagine a growing apex to be marked out 

 into a great number of successive narrow transverse zones, 

 beginning at the apex, each such zone will consist of cells 

 growing with a certain degree of rapidity which is not the 

 same as that of the zones on either side of it. Between the 

 zones which exhibit respectively the greatest and the least 

 rapidity of growth, there are a number of zones exhibiting 

 various intermediate degrees of rapidity. These facts may be 

 more clearly expressed by means of a formula. If the suc- 

 cessive zones of a growing apex are indicated as/...7V...A^+;tr, 

 the apical zone being /, the zone of most rapid growth being 

 N y and the last zone of the growing region being N+x, the 

 relation of their respective increments in the same time is 

 as follows: 



(apex) I<II<1U......<N*>N+I >N+x. 



maximum cessation. 



In intercalary zones of growth the same two regions are 

 to be distinguished, but in these cases the zone of cell-division 

 lies between two zones of active growth. This relation is 

 illustrated in the following table of some of Stebler's obser- 

 vations on the growth of the leaves of the Onion. 



The basal portion of the lamina and the upper portion of the sheath- 

 ing portion of the leaf were marked out into zones of 2*5 m.m. each, 



