224 RclatioiiH hetivcen Cilroirtlt and Eitrlroinuent 



Low efficiency indices were the rule from September to April^, nearly 

 all being below 5. During this period practically all the maximum tem- 

 peratures were below 65° F. (see Fig. 1) and although the sunshine curve 

 was much less regular than that of temperature all the weekly sunshine 

 totals were below 35 hours, seven being below 1\ hours (see Fig. 2). 

 During December the efficiency indices were very low and only varied 

 within small limits, being much the same in series of different ages, 

 which is not usually the case. This is evidently connected with the fact 

 that during December occurred the lowest grouj) of maximum tem- 

 peratures for the whole year, and the period also embraced the largest 

 group of low sunshine records. A rise in the indices began in January 

 coinciding with an improvement in both temperature and sunshine. 

 From March to August^ high efficiency indices, much over 5, were 

 obtained. Throughout this period the maximum temperatures were 

 above 65° F. except during the first four weeks when they were slightly 

 lower. Fifty per cent, of the weekly sunshine totals exceeded 35 hours, 

 the excess often being considerable, six totals being 50 or more hours, 

 while none ran below 1\ hours as happened earlier in the year. Thus 

 broadly speaking high efficiency indices are associated with high tem- 

 peratures and plenty of sun, while low indices occur in cold weather with 

 deficient light. 



Within this generalisation, however, more detailed information can 

 be worked out. 



An examination of the curves (Fig. 6) shows that during the greater 

 part of the year, from March to November, the efficiency indices rise 

 to their maximum very early in the life of the plant, usually within one 

 or two weeks from the close of the first period of growth. In sj)ring and 

 autumn this maximum efficiency index is not very great, in summer it is 

 much larger, but, given a moderate or plentiful supply of heat and sun- 

 shine, the impulse of the ])lant is to attain its maximum rate of growth as 

 early in life as possible. This, of course, tends to the production of larger 

 plants, as rapid growth at the beginning provides a large leaf surface at 

 an early date so that more assimilation and increase of material can take 

 ))lace. When plants are started in the wintei-, in December or January, 

 this ra])id lise to the maximum does not occur, but the etficiencv indices 

 slowly climb up, taking about five weeks from the end of the first growth 

 period to attain their maximum. This is associated with low nuixinuim 

 temperatures and low sunshine totals extending over the whole life of 



' Kir.st scries started in Se|i(eiiil)ei', last seiies ended in .\|ii'il. 

 - First series started in .March, last scries i-ndcd in Auj;tist. 



