10 ART. :î. T. ICHIMURA : ON THE FORMATION OF 



physiologically produced by the epinastic growth of the flower 

 stalk may from a biological point of view be described as a 

 phenomenon of " gamotropism."^^ Being exposed directly to the 

 sunlight, the lower side of the calyx, now in an nppermost 

 position, turns red beginning at the base and ending at the 

 periphery in a way just opposite to that observed in the case of 

 the upper side. The red colour on the lower side is not so bright 

 as it is on the upper side, but is rather dark except at the veinal 

 surface (Fig. 7.). Besides, the darkness of the red colour is in- 

 creased with the concentration of the spot and with the appearance 

 of green chlorophyllgrains. In the meantime, all parts of the 

 calyx-leaf on both sides, hitherto whitish, become noticeably green 



(Fig. 7,8.). 



Microscopical structure. — On the npper side the number of 

 red coloured epidermal cells and the intensity of the red colour 

 are both gradually increased. Some slightly blue cells are often 

 met with in the hypodermal layer. On the other hand, the red 

 cells on the lower side are mainly observal)le in its hypodermal 

 layer consisting of idioblastic irregular cells, Init partly also in 

 its epidermal layer, the cells of which mostly remain colourless. 

 Such colouration of the hypodermal cells may be characteristic 

 of the calyx-leaf of Japanese Hortense, for it is not usually found 

 in the flower-petals or petaloid calices of other plants, which 

 contain anthocyan. The multipolar horns of the idioblastic cells 

 of the entire mesophyll layer gradually become prominent and, at 

 the same time, the layer appears more spongy, the intercellular 

 spaces being more conspicuous. In the normally healthy state (i.e. 

 when not diseased or injured) the red idioblasts are confined to 

 the hypodermal layer and never go any deeper. This condition 



1) Ludwig, Fr.- Lehrbuch der Biologie der Pflanzen. 1895, ? 74. 



