SHELTERS ARE often necessary in experimental work with growing crops to protect research results from the influence of insects or insect-transmitted viruses or other diseases—without greatly altering the other important factors of environment such as light, soil and temperature. This article resulted from a study of the low sugar problem threatening cantaloupe production in several areas of the San Joaquin Valley. It describes a simple inexpensive framework covering a ground area 20 by 30 ft, and reports measurements of light, temperature and humidity within several such structures covered with various combinations of polyethylene and cheesecloth.