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Wheat seedlings (Triticum aestivum cv. Pacific Blue Stem) grown under continuous low‐level illumination were used to study the effects of pressure variation and its duration. Growth was determined by dry weights, leaf length, and types of secondary roots produced. Two sublethal shock pulses (1.41 and 2.82 kg cm −2) and three pressure duration intervals (0.1, 1.0 and 10.0 seconds) were studied. The results indicated a general overall reduction in growth associated with the shock pulse and that the pressure duration interval influenced the shock‐ growth response. The long pressure duration interval was found to be the most influential on shock pulse response. Present knowledge indicates that a pulse rise‐time of 1 ms and a pressure duration interval of at least 1.0 second affect plant growth at sublethal shock pulses, such that the growth response is linear or bi‐directional, depending on the magnitude of the shock pulses, and either linear or complex with respect to pressure duration interval for any shock pulse level. [ABSTRACT FROM AUTHOR]

Earlier studies on the growth requirements of isolated roots of barley and oats have been continued by using the culture methods already described. The investigation has included 3 problems. a. Effects of the method of sterilization. A comparision of autoclaving and sterile filtration in membrane filters after Zsigmondy on the following substances: glucose, sucrose, fructose and the accessory growth factors indole acetic acid, thiamin, and ascorbic acid. b. Effects of extracts of endosperm, roots and leaves of barley and oats, endosperm of pea, and bleeding sap of Carpinus. c. Effects of some nitrogen compounds, namely glutamic acid, asparagine, gelatine, peptone, and Casamino Acids (hydrolyzed casein). In most cases no promoting effects on the meristematic activity could be observed, but the added substances generally caused variation in root elongation. However, peptone in a concentration of 1 gm. per litre was beneficial to barley roots, which, when examined after 10 days' cultivation, had extraordinarily long meristem residues, and after 20 days some non-elongated cells also remained. The roots were thick and not very tapering. The other results indicated that the factors under investigation could not be responsible for the inhibited growth of roots of monocotyledons after isolation. The results with peptone indicate, however, that there is some definite growth factor lacking, and that the failure does not depend upon the internal constitution of the roots. Further it proved impossible to isolate the hypothetical growth factor from extracts of endosperm, roots and leaves of corresponding plants. The results with extracts from endosperm, however, indicated the presence of a water-soluble elongation factor, not of auxin character. Further studies are in progress. [ABSTRACT FROM AUTHOR]