The need for measurement of stomatal apertures arises in many kinds of investigations, including studies of gas diffusion through stomates

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Plant growth is characteristically depressed at certain levels of salt concentrations yet it sometimes responds to fertilizers even though growth depression can be expected to reduce nutrient requirements and even though fertilizer application increases salinity to some degree. This study was designed to examine tension zones involving interactions between nutrient supply (N and P) and salt concentrations. Grain sorghum (Sorghum bicolor (L.) Moench) was chosen for this study because it is commonly grown in regions of irrigated agriculture where soil salinity is often a problem. Plants were grown to maturity in automatically operated sand culture equipment at two levels each of N and P, each subjected to added Ca‐Na chloride salinity levels of zero, medium (EC = 10 mmho/cm) and high (EC = 20 mmho/cm). Vegetative growth was depressed to about 50% of control at both medium and high salinity, while grain production was depressed to about 35% at medium salinity and to almost none at high salinity. Chemical composition of leaves, in addition to familiar dilution effects and ion competition, revealed increased accumulation of Ca, Na, and CI related to high level of P supply, at high salinity only. When sorghum was grown at salinity levels that permitted reasonable grain production, maintenance of optimum soil fertility was important. However, the required level of nutrient supply was lower in saline than in nonsaline soils because of reduced growth. A critical balance between optimum nutrition and increased salinity from applied fertilizers was also involved.

PLANT PHYSIOLOGY bility is small and the response to red radiant energy is very reproducible. The material is easy to handle and manipulate. The assay is reliable between 103MAw/cm2 and 10 uw/cm2 of red (625 to 700 m,u) and the photoresponse is directly proportional to the logarithm of the irradiance.The technic consists of excision of the hook from 6-day-old seedlings of Black Valentine bean and exposure to red energy (625 to 700 m,u). The angle of hook opening is a quantitative measure of the photomorphogenic effect. The presence of bud, leaves or cotyledons, particularly the latter, causes an effect opposing the photoreaction, as does also 3-indoleacetic acid.The photoresponse increases with age of the seedling up to seven days, but at this age the hook has progressed up the stem close to the cotyledonary node; therefore, 6-day-old seedlings were found most suitable. In complete darkness no opening could be observed for 16 to 24 hours following excision; with red energy, the lag period was 4 hours and the subsequent opening was at a markedly increased rate as compared to the dark. The maximum opening in the red occurred at 250 C; in the dark at 300 C.

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