LIMITING FACTORS TO GROWTH MEASUREMENTS. 355 



work in the opposite direction to this primary temperature - 

 relation. For the causes suggested as well as for certain other 

 qualifications in the application of this rule, the whole of the 

 admirable discussion of the question in the original paper 

 should be consulted. It appears to me that this idea gives a 

 closer insight into the relation of growth to temperature than 

 we have hitherto been able to get. We may I think provision- 

 ally look upon the process of growth as the product of many 

 different chemical changes and syntheses each of which has the 

 above-named primary relation to temperature and that this 

 primary relation exhibits itself when other factors such as 

 water supply are not limiting the growth. This at any rate 

 gives a reason for such a case as the Agave inflorescence of this 

 paper, where growth was limited by temperature throughout 

 the whole range of conditions prevailing during the different 

 experiments. It may be taken as the primary reason also for 

 the general relation of growth to temperature which has been 

 established by so many observers. 



Temperature is no doubt also important in facilitating the 

 translocation of materials. This we know involves certain 

 organic chemical changes, starch for instance changing to 

 sugar in translocation, and such changes will go on more rapidly 

 at higher temperatures. Sachs (16) has shown that low 

 temperatures prevent the translocation of starch. He says 

 that on August 8, after a cool night, when the temperature at 

 sunrise was 9° C, the leaves of Phaseolus, Ampelopsis, and 

 Aristolochia Avere not completely cleared of starch. On the 

 morning of August 3 (temperature at 5 a.m., 8° C.) the leaves 

 of Dioscorea Batatas, Catalpa, and Moms were quite full of 

 starch. In October (morning temperature 6° C.) there was no 

 translocation in Nicotiana and very imperfect destarching in 

 Datura and Atropa. 



We see therefore why the temperature of the growing shoot 

 itself and not, except indirectly, the temperature of the 

 surrounding air should be the controlling factor in growth, for 



