Apr. 8, i9i8 Effect of Meteorological Factors on Sorghums 135 



the effect of freezing plants; very few of these, however, have considered 

 the effect of suboptimal temperatures on the retardation of growth. It 

 has been observed that the processes of metaboHsm become less pro- 

 nounced at low temperatures. This slowing up of the growth is due per- 

 haps to a decrease in enzymic action, as well as to the failure of the pro- 

 toplasm to function properly at such temperatures. 



Although light is necessary for the normal development of chlorophyl- 

 lous plants, but little is known regarding the effect of different intensi- 

 ties of light on their growth. Sachs (6) found that the rate of growth 

 in the seedlings of maize increases during the night and decreases during 

 the day, the period of greatest growth being early in the morning just 

 as it is becoming light. Smith (7), in testing Blackman's theory of limit- 

 ing factors, made an extensive series of growth measurements on the new 

 culms or growing shoots of bamboo. In all but one instance these meas- 

 urements showed a more rapid growth at night than in the daytime. 

 Smith concluded there were two factors which controlled the growth : (i) 

 temperature of the culm, and (2) supply of water to the culm. The sec- 

 ond factor, being intimately connected with the amount of water drawn 

 off by the transpiration of adult culms on the same rhizome, was in- 

 fluenced in its turn by two factors: First, the humidity of the atmos- 

 phere, and second, the intensity of the light. At night the greater 

 humidity of the atmosphere and the lessened transpiration due to the 

 absence of light both contributed to the certainty of an adequate supply 

 of water for the growing shoot. 



The measurements of Sachs and of Smith were made on growth pro- 

 duced from reserve food stored in the plant itself, and the results can not 

 be applied to the behavior of general farm crops like sorghum, for it is 

 known that in green plants the continued absence of light results in etio- 

 lation and eventually in a cessation of growth. A certain amount of 

 light is ordinarily required in the formation and functioning of chlorophyll. 

 Without sunlight the green plant is powerless to form new organic com- 

 pounds, and its growth in darkness comes about only through the trans- 

 formation of organic compounds already at its disposal. 



The observations of Linsser, Marie-Davy, and Angot, as noted by 

 Abbe (j, p. 211-290), show that there exists a decided difference in the 

 quantity of heat necessary for the development of the same species of 

 plants in different latitudes, and Marie-Davy asserts that the determin- 

 ing influence is the quantity of light which the plants receive. Abbe 

 (j, p. 79) also points to some work of Hellriegel with barley, in which it 

 was found that plants in the open air made a 50 per cent larger yield than 

 those grown inside a greenhouse in the direct sunshine, and fully three 

 times as much as plants grown in diffuse light under glass. 

 41812°— 18 5 



