On the Formation of Anthocyan in the Petaloid Calyx of the Red Japanese Hortense.

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1). When anthocyan has completed its development, chlorophyll-grains begin to appear in the mesophyll layer of the calyx and, at a later period, deposit a large amount of starch-grains. 2). After the appearance of the red colouration on the upper side, the flower-stalk nutates downward to expose its lower side directly to the sunlight. In this position, the lower side also assumes a reddish tinge. 3). The flower remains open for about four months in summer, and the calyx-leaf is persistent throughout this period. 4). Protanthocyan from which yellow, red, deep red, or bluish anthocyan and also bluish violet crystals are derived, consists of a certain colourless tannin compound. 5). Protanthocyan becomes yellow or green by alkalis. 6). In the red Hortense, the blue colour appears later than the red, and bluish crystals are often met with within reddish or purple cell0sap. Such variations as is well known depend on the different degrees of acidity. 7). The essential factors which bring about the change of protanthocyan into a coloured anthocyan in the red Hortense seem to be:- a). Sunlight. - Those calyx-leaves which are situated in the shade or a overlapped by others never become red. An exceptional case of rare occurrence in which the formation of anthocyan is independent of sunlight was observed by Zopf in the root of Parnassia palustris. Also the red pigment which occurs in such an underground organ as the sweet-potato or the red raddish seems to have little need of sunlight for its formation. b). Acidity. - It has been generally ascertained by previous observers that the red pigment can not exist without an acid cell-sap in the living state. The crystals of calcium oxalate with the aid of intercellular air-spaces may serve as a protecting medium to the delicate young calyx-leaf against strong sunlight, as they reflect the light and hinder a too speedy transpiration. Schimper states that leaves which have grown in the full sunshine are richer in crystals of calcium oxalate than those grown in the shade. But the calyx-leaf differs from ordinary green leaves in this respect, since these crystals are formed before chlorophyll granules appear. c). Tannin and sugar. - Many observations render it probable that the mother substance of anthocyan is a peculiar tannin matter. The calyx-leaf of the red Hortense, however, never produces red anthocyan in the absence of sunlight, though it contains tannin. The root of Parietaria diffusa produces red anthocyan only in its tannin idioblasts. Hence some plants appear to require light more than tannin, and others tannin more than light, for the development of anthocyan. The presence of sugar in the calyx-leaf of Hortense is observed only in the earlier phases of its development. Sugar may have no close connection with the formation of anthocyan. d). Mechanical injury. - Mechanical stimuli hasten the formation of ed anthocyan from protanthocyan. When the calyx surface is scratched with a nail, the injured part in a few days becomes much more intensely red than the healthy part. (Fig. 9.). This test is effective only in the later stages of the growth of the calyx-leaf. It is already known that any diseased or injured part of leaves or fruit may easily develope red anthocyan, and Molisch has recently observed a sudden development of a carmin red pigment on making a nail-scratch on the surface of a leaf of Schenckia blumenaviana. Ludwig and Linsbauer also noticed the formation of coloured anthocyan under the influence of mechanical injury. e). Soil. - The formation of anthocyan in the calyx of Hortense is probably more or less influenced by the nature of the soil. Schubler, Darwin, Molish, Miyoshi and others all ascertained that the colours of the anthocyan of Hydrangea-flowers are mush influenced by the chemical nature of the soil. DARWIN observed that alum directly influences the colour of Hydrangea-flowers. The chemical process that occurs in the conversion of protanthocyan into coloured anthocyan is, however, not yet cleared up. In conclusion, I wish to express my obligations to Prof. Miyoshi for his helpful advice during the course of my investigation.
1903-06-20

On the Formation of Anthocyan in the Petaloid Calyx of the Red Japanese Hortense.

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