CHAPTER 9 



Plants Grown under Controlled 

 Environmental Conditions 



Just previous to the planning and building of the Institute there were 

 several new developments in plant and animal physiology that indicated 

 the desirability of equipment for growing plants on a fairly large scale and 

 under a wide range of conditions as to light (quality, intensity and daily 

 duration), concentration of carbon dioxide, temperature, humidity, nitrate 

 supply, etc. The following may be mentioned as the more prominent of 

 these researches. In 1920 Garner and Allard " had published their monu- 

 mental discovery that day length initiated flowering in various kinds of 

 plants. Kraus and Kraybill 2" gave a new slant to the problem of reproduc- 

 tion in plants when they published their paper on the importance of the 

 proper balance between carbohydrate and nitrogenous substance in plants 

 as a determiner of fruit set and development. This paper focussed much 

 attention on the significance of the C/N ratio in plants. This ratio is of 

 course determined by the relative amount of photosynthesis on one hand, 

 and the amount of nitrogen compounds absorbed on the other; therefore, 

 all factors that affect these two processes in plants need consideration. 



Schanz ^"^ ^^ found evidence that ultraviolet rays may cause cataract by 

 coagulating the proteins of the crystalline lens of the eye, and that these 

 rays are of great importance in determining the form of plants. The injuri- 

 ous action ^° of ultraviolet was receiving much consideration. Before the 

 Institute was formally opened, Steenbock,^^ and Hess and Weinstock,i^ 

 had found simultaneously that ultraviolet rays impart antirachitic action 

 to various vegetable and animal materials. It turned out later that the 

 action of the ultraviolet rays was on one of the sterols, i.e., ergosterol. 



It has long been kno^vn that the carbon dioxide content of the atmos- 

 phere is too low to give maximum photosynthesis when other conditions 

 are at or near the optimum for this process. The experiments of H. Fischer, 

 Riedel, Jesse and others,^'*' p-^^^ just previous to 1920, indicated that crop 

 yields could be increased markedly in greenhouses and even outside by CO2 

 enrichment of the air; this of course increases the amount of photosynthe- 

 sis, as does longer daily illumination. Would it induce the flowering of 

 long-day plants as does the long day in accordance with the C/N ratio 

 conception, or is flower induction by day length due to a specific effect of 

 light quite independent of photosynthesis? 



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