Lecture 1 — 21 — Survey 



of the air that according to available criteria the 

 results in terms of plant yield and composition could 

 be reproduced within small limits of error. Thus, a 

 quantitative technique was established for various 

 types of physiological studies. 



In these experiments Mazda lights of high intensity 

 furnished adequate illumination for the growth of 

 wheat plants, even for the full cycle of development. 

 But for most kinds of plants tested, the Mazda lamp 

 illumination could not produce a satisfactory type of 

 growth. The quality of the light was especially at 

 fault. One recent trend in controlled chamber inves- 

 tigations is to employ various combinations of the 

 new fluorescent lights. Quality of spectrum may be 

 controlled to a considerable degree by combining fluore- 

 scent tubes of different colors, but often the problem 

 of sufficient intensity remains unsolved, although use- 

 ful studies may be made with the aid of these lamps. 

 Some investigators with sufficient funds at their dis- 

 posal have employed screened high-powered carbon 

 arc lights. Since most experiments must be conducted 

 in sunlight, the variability of the light factor is one 

 of the outstanding difficulties in the quantitative eval- 

 uation of plant nutritional processes. (See plates 6 

 and 7). 



Despite the importance of this consideration, even 

 without the complete control of light and temperature 

 environment, there still remain possible fruitful ex- 

 plorations into the effects of the aerial environment 

 on the growth of plants in relation to their nutrition. 

 This point may be illustrated by the experiments of 

 Thomas, Hill and their collaborators (1937). In- 

 genious apparatus has been constructed which makes 

 possible the growth of plants in small glass houses 

 with the automatic registration of CO2 utilized in the 

 sunlight, or produced in respiration during a dark 

 period. The natural fluctuations in light intensity and 

 temperature are measured at the same time. Control 



