Light in Greenhouse Culture 55 



winter months than the ordinary hothouse is able 

 to furnish. 



Pathological Relationship of Light 



While it is true that plants grow in the dark, they 

 must have light to thrive. The growth made in 

 darkness exclusively is of a soft nature. The long, 

 whitish, slender sprouts of potato kept in the dark 

 are a good illustration. Numerous diseases of plants 

 grown under glass may undoubtedly be traced to 

 improper light conditions. Cucumbers, for instance, 

 when grown in poorly lighted houses, become slen- 

 der, producing elongated petioles and stunted leaves 

 with little green color in them. Such plants, too, 

 are soft, and possess little of the solid or resistant 

 tissue. Poor light also makes cucumbers, as well 

 as most other hothouse plants, susceptible to mil- 

 dew, blight and leaf spots. Poor light and wet soils 

 are responsible for the burning of the foliage of 

 hothouse plants under fumigation. Too much light 

 often affects the transpiration of plants and causes 

 them to wilt unduly. Blossom end rot of toma- 

 toes under glass is more severe under bright light 

 than under partial shading. No fixed rules can be 

 given as to the light requirements of greenhouse 

 crops. Until more definite knowledge is obtained 

 on this important subject, the greenhouse manager 

 will of course depend on his common sense, observa- 

 tions and experience to guide him. 



