8i8 



MECHANICS OF GROWTH. 



Mean temperature. 



9-4^ C. 

 106 

 107 



II'O 

 II'O 

 1 I"2 



125 



Harting found that a Hop-stem, consisting of a number of internodes, which was 

 492 millimetres long on May 15th had attained by the end of August a length of 

 7-263 metres, this growth being distributed as follows over the different months : — 



0*492 metres in April. 

 2-230 May. 



2-722 June. 



1-767 July. 



0052 August. 



These observations and a number of others show that the grand period of 

 growth manifests itself even when the course of the changes of temperature acts in 

 opposition to it ; /. e. when the temperature rises while the rapidity of growth de- 

 creases owing to internal causes, and vice versa. The course of growth may no doubt 

 be so modified by great changes of temperature that the curve of the grand period 

 can no longer be recognised in the measurements. 



In order to determine the grand period of growth in a piece of a growing root, 

 internode, or leaf-stalk, it is sufficient to mark a zone of the organ at the part where 

 elongation is beginning by two lines of Indian ink, and to measure the daily (or 

 half daily) growth of this piece until it ceases. 



By applying this method to the primary root of Vicia Faha, the temperature 

 varying each day between 18° and 21*5° C, I found the following increase to take 

 place in each period of twenty- four hours in a piece originally i mm. long situated 

 immediately above the punclum vegetationis : — 



