192 GROWTH 



the growth rate is diminished by the dislocation of the meta- 

 bolic processes. If this contention be correct, a close corre- 

 lation between the length of the root and the time of the 

 incidence of the second maximum should obtain. 



In further illustration of the interaction of temperature 

 with other factors, the work of Bushnell, Tottingham and 

 Gregory may be referred to. Bushnell * examined the growth 

 of the potato in controlled conditions at temperatures vary- 

 ing between 20° to 29 C. Both the leaves and the tubers 

 decreased in size with increasing temperature, no tubers being 

 formed at 29 C. Respiration in the sub-aerial parts also in- 

 creased with rising temperature, which means a greater con- 

 sumption of carbohydrate and thus a reduction in the amount 

 of material available for translocation which roughly corre- 

 sponded to the reduction in tuber growth in the experimental 

 conditions employed ; for although the carbon dioxide of 

 respiration during the day is immediately available for re- 

 synthesis, that emitted during the night is not. It thus ap- 

 pears that the excessive respiration at higher temperatures is 

 an important factor, if not the limiting factor, in the growth 

 of the potato. 



Tottingham f studied the effect of temperature and light 

 on the growth of the wheat plant. When the light intensity 

 is low a lower temperature is favourable to the production of 

 dry matter, and in these conditions the tissues show a higher 

 percentage and yield of protein. When the light intensity 

 is high and the temperature low, young plants contain more 

 sucrose and protein and mature plants contain more carbo- 

 hydrate and give a higher yield of grain : at higher tempera- 

 tures the percentage of protein is increased, although the total 

 amount may be less owing to the increased loss of carbohy- 

 drate due to the more intense respiration. 



Gregory, J in continuance of his study of the energy re- 

 lations of plants, has investigated the effect of temperature 

 on the increase in the area of the leaf surface of Cucumis sativus. 



* Bushnell : " Univ. Minn. Agric. Exp. Sta.," Technical Bull. 34, 1925. 

 f Tottingham : " Plant Physiol.," 1926, 1, 307. 

 $ Gregory : " Ann. Bot.," J928, 42, 469. 



