7i^ 



MECHANICAL LAWS OF GROWTH. 



April 



March 28 

 29 

 30 

 31 

 I 

 2 

 3 

 4 

 5 

 6 



7 

 8 



9 

 10 



Normal plant 

 in the light. 



io*6 mm. 



103 



6-3 



47 



5-8 



4*4 



3'8 



2*0 

 I'2 



0-7 

 00 



Etiolated plant 

 in the dark. 



14*2 mm. 



12*6 



15-9 

 i6-6 

 18-2 



15-5 

 i4'o 

 13-8 

 11-9 



8-8 

 4'4 



2-1 



0-6 



0"0 



Mean temperature. 

 i4-3°C. 



12*4 

 I2*0 

 II'2 



io*7 



IO*2 



9'4 

 IO-6 

 io"7 



II'O 

 IIO 



112 

 11-5 

 12-5 



An internode of Humulus Lupidus gave — 



Increase of length 

 in 24 hours. 



April 22 19-0 mm. 



23 



24 



25 

 26 



25-0 

 260 



172 



4-8 



Mean 

 temperature. 



149° c. 



i4"5 



14-3 



i3'9 



141 



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 Jun«. 



1-767 July. 



0-052 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 ; i. 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 

 growth begins 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 i8° and 2r5°C., I found the following increase to take 



