Respiratory Chromogens [stub]

William Crocker
1909 Botanical Gazette  
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more » ... ntent at JSTOR is a digital library of academic journals, books, and primary source objects. JSTOR helps people discover, use, and build upon a wide range of content through a powerful research and teaching platform, and preserves this content for future generations. JSTOR is part of ITHAKA, a not--for--profit organization that also includes Ithaka S+R and Portico. For more information about JSTOR, please contact 1909] CURRENT I.TERA TURE 83 morph in a heterozygous condition, the homozygous giving unmottled seeds. This peculiarity results in a new ratio, i8: i8:6:6: i6, instead of the anticipated 27:9:9:3: i6. Latency is held to mean invisibility and not inactivity or dormancy. BATESON'S "presence and absence" hypothesis, in which the presence of any character is said to be dominant to its absence, is believed to be of general validity; and hisI' more recent terms "epistatic" and "hypostatic," as applied to the capacity of one unit to hide or be hidden by another, are accepted. Thus in MENDEL'S original case, yellow in cotyledons is not to be considered "dominant" over green, but dominant to the absence of yellow and "epistatic" to green, i. e., according to SHULL, causing its "invisibility" but not its "inactivity." This change of view involves some nice distinctions, but appears to obviate some of the difficulties of the older view of dominance, especially in connection with ontogeny. Incidentally all that remains of the Mendelism of MENDEL is his hypothesis of gametic purity. The superstructure erected upon this has grown in complexity with great rapidity. With latency thus clearly defined, four types of latency are discussed: (i) "Latency due to separation, in which an allelomorph when acting alone has no external manifestation, and is only rendered patent by combining it with another allelomorph. " This type of latency is not uncommon, and gives rise to such ratios as 9:3:4, 9:7, 27:9:28. (2) "Latency due to combination, in which two dominant allelomorphs, each giving rise to a peculiar character when acting alone, lose their external manifestation when coexisting in the same zygote." This gives the ratio first mentioned above in mottled beans, and may account for certain "midraces." (3) "Latency due to hypostasis, in which the presence of one allelomorph cannot be detected owing to the presence of another allelomorph, the character produced by the latter being unmodified by the activity of the former." For example, a black bean is shown to hide a distinct-brown allelomorph, and a dark orange bean to carry invisibly a light-yellow allelomorph. This condition may give such a ratio as I2:3:I. (4) Latency due to fluctuation. Disappearance of characters under unfavorable conditions of nutrition, etc.; a very common phenomenon which may cause discrepancies from the expected ratio. Some of the cases formerly called "incomplete or partial dominance" would probably be classed here. Ratios may also rarely be modified by the failure of certain allelomorphic combinations to form a zygote which will develop.-R. R. GATES. Respiratory chromogens.-PALLADIN'4 has devised a new, very simple, and effective method of detecting the respiratory chromogens in plants. He uses this method to show the wide distribution of these chromogens in the plant kingdom. In 7I species, ranging from liverworts to dicotyledons, this method showed these I3 BATESON, WILLIAM, Facts limiting the theory of heredity. Science 26:649-66o. I907. '4 PALLADIN, W., Die Verbreitung der Atmungschromogene bei den Pflanzen. Ber. Deutsch. Bot. Gesells. 26a:378-389. I908. I5 PALLADIN, W., Ueber die Bildung der Atmungschromogene in den Pflanzen. Ber. Deutsch. Bot. Gesells. 26a: 389-394. i908. i6 WINKLER, HANS, Ueber Propfbastarde und pflanzliche Chimaren. Ber. Deutsch. Bot. Gesells. 25:568-576. figs. 3. 1907.