44 AGRICULTURAL RESEARCH AND THE FARMER : 



tions which can be easily controlled by the grower. The 

 cucumbers are grown in pots in an experimental glasshouse so 

 constructed that it is possible to control, and to keep constant, 

 the conditions of humidity, light intensity, and temperature. 

 In the series of experiments carried out from 1919 to 1921 the 

 humidity and light intensity have been kept constant throughout, 

 while the temperature has been varied for each experiment. 

 The hght is supplied by means of powerful electric lamps over- 

 hanging the pots. The first experiment was conducted at a 

 temperature of 95° F., and it was found that the plants grew 

 less and less rapidly, and stopped growing after a fortnight. 

 This was curious, for in commercial practice the temperature of 

 cucumber houses often reaches 120° F. It was important to 

 find out why the falling off in growth had taken place. There 

 were three alternatives; either the temperature was too high, 

 or the light intensity was too low, or the effect of continuous 

 light was bad. Subsequent experiments were therefore carried 

 out at increasingly low temperatures, and as the temperature 

 was lowered the growth improved. Already a temperature of 

 75° F. has been reached, and the rate of growth has not yet 

 reached its maximum. Thus there is clearty some factor detri- 

 mental to growth which increases with the temperature of the 

 house. Exactly what that factor is, further experiments now 

 in progress will doubtless discover. 



In another set of experiments, the effect of varying light 

 intensity was studied, and it was found that the greater the 

 light the greater the growth. If this is confirmed by further 

 work under varying conditions it should have an important 

 practical application, inasmuch as it will show that cucumber 

 growers should aim at a high degree of light intensity, especially 

 during the winter months. An inference of this kind had 

 already been drawn from the results of a test made at Cheshunt 

 in a new greenhouse of a cucumber grower in that district. The 

 rate of growth of the cucumber plants in their early stages was 

 more than doubled in the new houses compared with the old; 

 after six weeks the plants in the new houses were about a fort- 

 night ahead of the others. The explanation probably was that 

 the new house, instead of facing north and south like the old, 

 faced east and west, with a steep roof sloping to the -south, so 

 that the rays of evening or winter sunlight struck the roof almost 

 at right angles and reached the plants instead of being mainly 

 reflected as in the case of the old houses. The study of the 

 effects of light intensity at the Institute is now being extended 

 to test whether continued light has any beneficial effect. The 

 results of this work may be also, of course, of practical importance. 



