1913.1 PUBLIC DOCUMENT — No. 31. 61 



THE INFLUENCE OF VARIOUS LIGHT INTEN- 

 SITIES AND SOIL MOISTURE ON THE 

 GROWTH OF CUCUMBERS, AND THEIR 

 SUSCEPTIBILITY TO BURNING FROM 

 HYDROCYANIC ACID GAS. 



G. E. STONE. 



The influence of light on photosynthesis, structure and devel- 

 opment of plants is well known to plant physiologists, but is 

 too little appreciated by growers of crops, whether under glass 

 or in the field. It is also well known that plants grown in the 

 dark are pale and slender, with undeveloped leaves, and they 

 quickly wilt and die when exposed to different temperatures 

 and light conditions. The variations in light intensity in the 

 greenhouse or in the field, such as occur in periods of cloudy 

 weather, affect crops greatly. There are many features con- 

 nected with greenhouse construction, such as inferior or dirty 

 glass, angle of the roof, heavy shadow-casting frames and others 

 which also play an important part in plant development. Cer- 

 tain light-requiring crops grown under the inferior light condi- 

 tions of November and December develop abnormally, and often 

 suffer greatly from wilts in the spring when the light is more 

 intense. The plants possess light-colored, thin leaves, elongated 

 and slender internodes and leaf petioles, and, in fact, are in a 

 state of partial etiolation. 



Light inhibits growth and has a remarkable effect on the tex- 

 ture of plant tissue. While it has a great deal to do with the 

 non-ripening and ripening of wood, moisture, temperature and 

 other factors also enter in. 



The successful growing of lettuce under glass requires excep- 

 tional skill, as much attention has to be given to the influence 

 of light, moisture and other factors on the crop to prevent what 



