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THE IMPORTANCE of thiamin (vitamin B1) for growth of roots has been described by several investigators (Kogl and Haagen-Smit, 1936; Bonner, 1937; Bonner and Axtman, 1937; Robbins and Bartley, 1937). Vitamin B1 and certain other compounds such as nicotinic acid and vitamin B6 (Bonner and Devirian, 1939; Robbins and Schmidt, 1939), are essential for growth of roots in vitro. Some roots, if not all, are unable to synthesize thiamin when grown in cultures detached from the shoot. The evidence indicates that thiamin is a true phytohormone, made in illuminated green shoots and translocated into the roots where it promotes growth (see Bonner and Greene, 1938). Recent papers by Bonner and Green (1938, 1939) and by Bonner and Bonner (1940) have reported that growth of numerous species of plants is promoted by small amounts of thiamin added to soil or sand in which the plants are grown. It appears, furthermore, that thie response of a given kind of plant to additions of the vitamin may be regulated, at least in part, by the amount of thiamin synthesized in the leaves. The number of contributions to this new subject is mounting rapidly, but as yet there is little information available concerning the factors which influence production and use of thiamin in plants. Pfiitzer, Pfaff, and Roth (1938) have stated that barley supplied with nitrogen fertilizer contained appreciably greater amounts of thiamin than plants grown in soil deficient in nitrogen. Von Kuthy (1937) pointed out the existence of a parallelism between thiamin content and the nitrogen present in cereal grains. Apparently the thiamin content of cereal seeds decreases during germination in the dark (Von Kuthy, 1937) and is formed in green leaves only in the presence of light (Hlavaty, 1929). A variety of methods has been worked out for the quantitative determination of thiamin; references to these may be found in the books by Williams (1938) and by Harris (1938). One very sensitive method, developed by Schopfer and Jung (1937), involves the use of the fungus Phycomyces Blakesleeanus which requires an external supply of thiamin or its components. It has been pointed out by Bonner and Erickson (1938) that the use of pyrimidine and thiazole components by Phycomyces does not invalidate its use in assays for "thiamin activity" in investigations concerning growth of higher plants, since the |
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