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There has been marked disagreement among plant physiologists relative to the effectiveness and importance of transpiration in cooling the leaves of plants. SMITH (12), CLUM (4), CURTIS (5), and others have concluded that the cooling effect is slight and rarely of importance in preventing excess heating, whereas, SHULL (10), EATON and BELDEN (7), ARTHUR and STEWART (1), CLEMENTS (3), and others have concluded that the cooling effect may be great. The latter investigators especially have claimed that the cooling effect is much greater than is commonly recognized. ARTHUR and STEWART, and CLEMENTS have claimed that the excessively high temperature of leaves, when they are inclosed in cellophane envelopes, or in glass chambers and exposed to strong light, is due to the fact that the cellophane or the glass effectively stops transpiration; while the failure of wilted, or vaselined leaves to rise in temperature more than 2°to 5°C. above those not so treated is due to the ineffectiveness of these treatments in preventing transpiration. As the writer pointed out in a recent paper (6), however, these investigators overlooked the fact that glass and cellophane are heat traps permitting the passage of visible radiation, but preventing much of the loss of heat by interfering with cooling by air currents, as well as by reducing loss by radiation in the infra-red. It was found that dry black paper showed similar marked rises in temperature when inclosed in cellophane envelopes, and in this case evaporation could play no part.Although the effects of various factors upon leaf temperatures have been investigated by several workers, almost no attention has been given to the loss of heat by radiation in the infra-red. BROWN and ESCOMBE (2) speak of loss of heat by emission, and include loss by both conduction and radiation. In their preliminary discussion of a hypothetical case they state that the walls of the inclosure must be at the same temperature as the inclosed air, but, in the actual experiments cited, no mention is made of the wall temperature, and it is assumed that the air temperature is the same as that of the leaf 's surroundinas. It is also assumed that if the air temperature is equal to or exceeds that of the leaf, there will be no loss of heat from the leaf by radiation. They, WArATSON (13), and other investigators seem to have failed to realize, that the oxygen and nitrogen of the atmosphere are almost transparent to radiation in the infra-red, and that in such an atmosphere leaves may become cooler than the air about them, owing to radiation

The ability to taste 6-n-propylthiouracil (PROP) is genetically determined. PROP tastes moderately bitter to 'medium tasters' (MT), intensely bitter to 'supertasters' (ST), and tasteless to 'nontasters' (NT). The psychophysical method used to characterize PROP status should capture the entire range of perception, while minimizing context, ceiling and other effects. Magnitude estimation successfully captures the variability in PROP perception, but requires normalization and may be difficult to conduct in industrial settings. Two labeled scales were tested as part of three separate studies (S1, S2 and S3) to measure perceived intensity of PROP and sweeteners. All studies included reportedly healthy volunteers aged 21-62 years recruited at Cultor Food Science in Groton, CT. In S1 [n = 163 (55 males, 108 females)], subjects rated perceived intensity of PROP-saturated paper and sucrose (1.0 M) on the Labeled Magnitude (Green) Scale (LMS) [labeled line with descriptors (no taste--strongest imaginable)]. In S2 [n = 152 (49 males, 103 females)], subjects rated perceived intensity of sucrose (1.0 M) and PROP solutions (0.001 M, 0.0032 M) on the LMS. In S3 [n = 136 (48 males, 88 females)], subjects rated perceived intensity of sucrose (1.0 M) and PROP solutions (0.001 M, 0.0032 M) on a 9-point category scale (1 = not at all; 9 = extremely). In all experiments, water rinses were included between each tastant and PROP was the final stimulus. Statistical analyses included descriptive statistics, regression analysis, and ANOVA. In S1 and S2, those with higher PROP perception perceived sucrose more intensely [(S1: r = 0.32; p < 0.001); (S2: r = 0.25; p < 0.01)]. A higher frequency of females were ST than males. Also, the PROP effect on sweet perception was most evident in female ST. This apparent sex difference may be the result of hormonal variation associated with menstruation. As well, in S1 and S2 subjects aged 20-40 years, females had significantly greater variance among sucrose intensity ratings than males (F = 3.66; p < 0.01), which may be due to hormonal changes with menses. The S3 results failed to show either the positive correlation between PROP and sucrose perception or the sex difference. Thus of the two labeled scales, the LMS appears to be better for assessing PROP perception, as it is continuous and also minimizes ceiling effects. Future research will extend these studies by including sucrose and high intensity sweetener concentration series.

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