Volume VI APRIL, 1920 No. 4 



ON THE RELATIONS BETWEEN GROWTH AND 

 THE ENVIRONMENTAL CONDITIONS OF TEMPE- 

 RATURE AND BRIGHT SUNSHINE. 



By WINIFRED E. BRENCHLEY, D.Sc. 

 {Rothamsted Experimental Station.) 



(With 13 Text-figures.) 



It is fully recognised that the amount of growth made by any crop in 

 the field and the rate at which maturity is reached is influenced by many 

 factors such as temperature, rainfall, season, sunlight, soil conditions 

 and available plant food. There is, however, little definite information 

 as to the influence of each of these factors on a plant at various stages 

 of growth nor with regard to the changes in the actual rate of growth at 

 difl'erent periods from the seedling to the mature plant. 



It is difl&cult or even impossible to gain this information from crops 

 growing under normal conditions in the field, because some of the factors 

 cannot even be measured with any degree of accuracy and all are so 

 intimately associated that the action of one or other can hardly be 

 disentangled from the rest. Simplification is therefore essential and some 

 method must be adopted whereby certain of the factors are controlled 

 and kept as constant as possible, thereby reducing the number of the 

 variable influences to be observed. The method of water culture was 

 therefore used, as it enables a strict control to be placed on the food and 

 water supplied, it permits of the roots being observed and weighed with 

 far greater accuracy than in soil experiments, and its compactness 

 allows of a large number of plants to be given individual treatment at 

 the same time. It is also possible to keep a close watch on the tempera- 

 ture variations to which the plants are subjected and to observe the 

 effect of these variations on a number of individuals at different stages 

 of growth. 



Environmental Conditions. 



The experiments were carried out in a roof greenhouse specially 

 constructed for water culture work and extended over a period of 

 sixteen months from September 1915 to January 1917. As Rothamsted 



Ann. Biol, vi 15 



