TO the new number of Prof. Cohn's publication Dr. Max Scholtz contributes an interesting paper on the nutation of the flower-stalk in poppies and of the terminal shoots in Virginian creeper. In both cases the nutation is dependent on the action of gravity, but has nothing to do with the weight of the bud. In the case of poppies the downward curvature of the stalk takes place with sufficient force to lift a weight equal to twice that of the flower-bud. If, however, the flower-bud be removed there is no longer any nutation; the stalk straightens itself. Vöchting had already shown that this is the case even if the amputated bud is tied on again with thread. Dr. Max Scholtz further states that if a weight three times as heavy as the bud is substituted for it, the stalk still straightens itself, and lifts up the weight. The state of the case then is this: the upper part of the flower-stalk, during a certain stage of growth, is in a high degree positively geotropic if it remains in connection with a developing flower-bud, but not otherwise. The author has further succeeded in determining the exact part of the flower-bud which governs the geotropism of the stalk. If the pistil is excised, nutation ceases, the stalk becoming negatively geotropic; but if all the other whorls of the flower are removed and the pistil left, then nutation goes on as usual. But beyond this, if the ovules are extirpated, but the wall of the ovary left standing, the nutation is stopped. Hence we arrive at the striking conclusion that the presence of developing ovules in the young ovary determines the reaction of the flower-stalk towards gravity. A certain analogy is obvious with the irritability of root-tips, investigated by Darwin. Dr. Max Scholtz's observations afford a good example of the extreme complexity of those phenomena of growth which a few years ago were thought susceptible of a simple mechanical explanation. The author thinks that the nutation is of advantage, inasmuch as the reversed position of the flower-bud allows a better access of light to the developing ovary. As is well known, the flower-stalk ceases to nod when the flower opens; in other words, as soon as the development of the ovules is completed the flower-stalk becomes as strongly negatively geotropic as it had been positively geotropic before.
Beiträge zur Biologie der Pflanzen.
Herausgegeben von Dr. Ferdinand Cohn. Band 5. Heft 3. 1892.
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