CUCUMBER 337 
various descriptions. See page 400 for cultural directions. 
Insect enemies.—Various insects feed on greenhouse 
cucumbers. One of the most serious pests is the red 
spider. Methods of control are discussed on page 123. 
Unless preventive means are employed, the white fly 
often appears in such numbers as to inflict heavy losses. 
Either potassium or sodium cyanide gas may be used to 
check the ravages of this insect before its depredations 
have become serious. Full instructions for their use are 
given on page 109. 
Interesting experiments were made by Stone and 
Thomas at the Massachusetts station, relative to the in- 
fluence of various light intensities and soil moisture con- 
tents on the development and character of cucumber 
plant tissues. Plants which received the least light and 
the most water were soft and tender and much more sus- 
ceptible to injury from hydrocyanic gas than were plants 
which received full light and normal amounts of water. 
The investigators emphasize the importance of noting 
the condition of the plants before proceeding to fumigate 
with cyanide. If cloudy weather and perhaps high 
temperatures have prevailed for a few days and the 
plants have been supplied with an abundance of moisture, 
the tissues will be soft and tender, and injuries will be 
much more likely to occur than when the fumigation 
follows several days of sunshine and normal conditions 
of heat, humidity and soil moisture. Growers will do 
well to consider these factors before fumigating their 
houses. 
The nematode is regarded by most growers as one of 
the worst pests of greenhouse cucumbers. Sterilization 
with steam is the usual method of controlling this enemy. 
See page 116. 
The aphis is also an enemy of greenhouse cucumbers. 
For methods of control, see page 119. 
Fall and spring plants are often attacked by the com- 
