Lecture 5 — 119 — Artificial Media 



ture conditions. In summer in Berkeley the environ- 

 ment has been so favorable (adequate light and rela- 

 tively low night temperatures, preventing excessive 

 respiration) for the operation of these factors in 

 growing tomato plants that extremely fruitful plants 

 have been produced, even when nitrogen was supplied 

 to the full extent of the plant's capacity to absorb 

 nitrogen. Under another climatic complex a different 

 conclusion might be reached. The indispensability 

 of appraising the mineral nutrition of the plant with 

 reference to carbohydrate synthesis is well exemplified 

 by the investigation of Nightingale (1942) in Hawaii 

 on the pineapple plant and that of Clements on sugar 

 cane. These relations are of importance even though 

 modern research reveals the significance of hormone 

 factors in the initiation of flower buds and in determin- 

 ing other physiological processes. 



Nutrition of Plants in Soil and in Artificial Culture 

 Solutions : — I have surveyed some of the physiologi- 

 cal aspects of the inorganic nutrition of plants as 

 they are offered for examination under the controlled 

 conditions of artificial culture technique. I do not 

 think that there is reasonable doubt that by experi- 

 ments of this kind we do gain an insight into certain 

 plant processes that is of great service in understand- 

 ing the nature of the soil-plant system. Yet the role 

 of soil colloids in plant nutrition intrudes when we 

 attempt a too direct and simple application of the 

 results of artificial culture experiments to the growth 

 of plants in a soil medium. After all, the union of 

 the absorbing root organ and the soil colloid is a 

 very close one and contact effects of one kind or another 

 are inevitable. In an aerated solution or in a sand 

 culture through which a nutrient solution is flushed 

 from time to time the nutrient ions are brought to 

 the roots. In the soil the roots explore the soil, and 

 develop enormous areas of root surface under favor- 



