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due to ihe degree of transparency of the glass caused by uncleanli- 

 ness. From the results obtained in the Station house and from the 

 many observations made in regard to the abnormal eftects in those 

 houses which made use of double glass, redetermined to make some 

 experiments which would otYer more conclusive proof as to the rela- 

 tive merits of single and double lights of glass of various degrees 

 of transparency, as affecting leaf assimilation or photosynthesis. 

 Experiments of this nature would not be necessary to convince a 

 phvsiologist. since the results of light starvation are too well known. 

 Among certain growers the case is different. 



Before passing on to a description of these experiments and their 

 results, it would be well to briefly call attention to some matters con- 

 nected with photosynthesis. Plants are dependent upon two sources 

 for their food : namely, the soil and the air. The food which plants 

 take from the soil consists of nitrogen, potash, phosphoric acid, etc., 

 which, in order to be available as food, must be exceedingly dilute, 

 and the same holds good, or at least such are the conditions as 

 regards the carbon dioxide which is obtained from the air. Most 

 cucumber growers, however, appear not to realize that over ninetv 

 per cent of the plant's food comes from the air and that assimilation 

 of this food, which consists of carbon dioxide, requires the action 

 of sunlight. Neither are they aware that photosynthetic activity 

 increases proportionally to intensity of light. Furthermore, the 

 activity with which carbon dioxide is as'similated depends not only 

 upon the intensity of the light, but upon the position of the 

 leaves. Cucumber leaves arrange themselves upon the stem in such 

 a manner that light strikes them at the most favorable angle for 

 carbon assimilation. In this respect training them on a trellis in a 

 greenhouse during the winter is desirable, as it enables the light to 

 act on the leaves to the best advantage. Growers, however, do not 

 realize that a plant which grows as rapidly as the cucumber and 

 which displays its large leaves at the most suitable angles and posi- 

 tion for the rays of light, has any especial need for carbon assimila- 

 tion. They seem to imagine that, if the soil contains a sut^cient 

 amount of plant food, that is all that is required e.xcept heat, and 

 the matter of light is of comparatively little importance. It is not 

 only a bad policy but contrary to all experimental knowledge and 

 common sense to substitute heat for light as a growth stimulus, and 



