. The Biological bulletin. Biology; Zoology; Marine biology. PHOTOTROPIC RESPONSES OF AVENA 309 falls in two distinct and regular steps from the neighborhood of 30 minutes to about 13 minutes, then rises steeply. In the intensity range producing the rise in reaction time the shoot, after bending for about 9 minutes, very abruptly stops bending toward the light and begins bending away from it. Averages of four such responses at two intensities were recorded as follows: at log / = , r. t. = ; at log / = , r. t. = These are probably the negative responses observed by Arisz (1915
. The Biological bulletin. Biology; Zoology; Marine biology. PHOTOTROPIC RESPONSES OF AVENA 309 falls in two distinct and regular steps from the neighborhood of 30 minutes to about 13 minutes, then rises steeply. In the intensity range producing the rise in reaction time the shoot, after bending for about 9 minutes, very abruptly stops bending toward the light and begins bending away from it. Averages of four such responses at two intensities were recorded as follows: at log / = , r. t. = ; at log / = , r. t. = These are probably the negative responses observed by Arisz (1915) at intermediate intensities, the response sequence observed by him with increasing intensity being positive—positive followed by negative— 2 3 Log Intensity—Meter-Candles Fig. 2. Relation between log intensity of white light and reaction time. Each point is the average of 10 readings (Table I). Open circles, coleoptiles as a whole. Solid circles, bases shielded. Triangles, tips shielded. Descending curves are hyperbolas derived from the data. Ascending curves are theoretical. The double relation between reaction time and intensity secured here is very likely an expression of the tip and base growth responses reported by Went. At 500 meter-candle-seconds, Went obtained a double growth response from the naked plant, one after 8 minutes and the other after 28 minutes. At this intensity (log I = ) the average reaction time in my experiments is minutes, only the earlier responses being recorded. Efforts to observe the expected second bending yielded such variable results that they were abandoned in favor of the procedure described in the next Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Lillie, Frank Rattray, 1870-1947; Moore, Carl Richard, 1892-; Redfield, Alfred Clarence,
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectb, booksubjectzoology
