THE RELATION OF LIGHT TO GREENHOUSE CULTURE. 



by 

 GEORGE E. STONE. 



The greenhouse industry at the present time is at such a high 

 state of perfection as compared with former days that the la\Tnan 

 would have small idea of the skill attained in growing crops under 

 glass. The grower can now control the en\-ironment of his crops 

 so largely as to eliminate many troubles formerly common. 



There is no factor associated vsith the construction and manage- 

 ment of the greenhouse which does not possess a bearing on crop 

 production. Heat, light and moisture are especially important, 

 and the size and direction of the house, amount of air space, sys- 

 tem of ventilation, size, quality and angle of the glass, purlins, 

 posts, etc. are also important, as are air and soil moisture and the 

 physical, chemical and biological features of the soil. Although 

 a great deal is known concerning the influence of these factors 

 upon plant growth, there is still much to be learned. The knowl- 

 edge already gained has come from the long experience of an un- 

 usually skilled class of growers. ]\Iuch of it is intuitive and diffi- 

 cult to impart to others. In man}- instances no definite reason 

 can be given for certain practices. 



The evolution of the modem greenhouse from the older types 

 has resulted in a marked change in greenhouse management, 

 which has brought about the use of larger glass and larger houses, 

 and a relative decrease in the size of the framework (made possible 

 by the introduction of iron) , or an}i:hing tending to produce shade. 

 As a consequence of this improvement in greenhouse construction 

 crops are grown better and more cheaply, for in these large, well 

 lighted houses they are less exposed to sudden changes and are 

 consequently less susceptible to disease. 



The investigations described in this bulletin* have a bearing 

 on greenhouse construction and management, for the problem of 

 light is one of the most important from the physiological and patho- 

 logical standpoint. While greenhouse construction has progressed 

 along scientific lines vdth the help of skilled builders and intelli- 

 gent growers, it has by no means reached its limit of development ; 

 and man}- false ideas of the relation between certain greenhouse 

 conditions and the type of construction are still held. 



These experiments have been carried on for some years, and 

 credit should be given to IMr. Neil F. IMonahan, assistant for some 

 time in the laborator}-, for many of the experiments outlined, as 

 he super\'ised the work. Mr. G. H. Chapman also made a few 

 records for us, and Mr. S. C. Brooks did some of the experiments 

 under different conditions. Some valuable tests were also made 



♦These were done in p.irt on the Adams Fund under the heading — "Relation of Meteoro- 

 ogical Conditions to Plant Growth and Diseases." 



