102 



In conclusion it can be said that the 

 investigation of the environment in re- 

 lation to plant growth and develop- 

 ment, as carried out in a phytotron, 

 yields results of such practical and 

 theoretical significance, that its costs 

 are offset many times by the results ob- 

 tained in it. In a phytotron we just ap- 

 ply the principles which have guided 

 physical and chemical research for so 

 manv decades— namely, carrying out 

 work under rigidly controlled and re- 

 producible conditions— to research with 



PHYSIOLOGY 



plants. Actually, from the standpoint 

 of research efficiency, there is no good 

 reason any more for carrying out ex- 

 periments with plants in ordinarv un- 

 conditioned greenhouses. For the re- 

 sults have a low degree of significance 

 due to great variability of the experi- 

 mental plants and poor reproducibility. 

 Fortunately this is becoming generally 

 recognized and a number of plant 

 growth chambers with proper control 

 over the environment have been con- 

 structed or are being planned. 



QUESTIONS 



1. List five external environmental fac- 

 tors which affect plant growth. 



2. What environmental study is not as 

 active as some others, according to Dr. 

 Went? Why is this so? 



3. What effect does a controlled environ- 

 ment have on plant variability? 



4. Mention some of the results obtained 

 in the Earhart Plant Research Labora- 

 tory. 



George W. Gray 



Our Bridge from the Sun 



Reprinted with the permission of Mrs. A. 

 Gray from Harpers Magazine 211(1264) :64- 

 71,1955. 



Man lives in two worlds. There is the planetary structure; the waters of 



first the older, larger, less complicated rivers, lakes, and seas; and the oxvgen, 



realm of inorganic matter— stars, inter- nitrogen, and rarer gases of the atmos- 



stellar gas and dust, planets, and the phere. This is the physical world, and 



rocks, metals, and other minerals of matter in such forms apparently con- 



