MR. A. J. EWART ON ASSIMILATORY INHIBITION. 445 
that (1) as the red colour disappears and the chlorophyll grains 
become green, starch becomes more abundant in the chlorophyll 
grain, because light now exercises its full inhibitory action upon 
the translocation of starch; (2) young red leaves of Quercus 
pedunculata &e. contain plenty of starch before the chlorophyll 
grains become green, the starch being derived by excessive trans- 
location from the parent plant, owing to the rays inhibitory to 
translocation being cut off; and (3) in red light starch is formed 
in the mesophyll but not in the palisade parenchyma, owing to 
the red light allowing more rapid translocation from the palisade 
parenchyma cells. The abundant formation of starch in the 
chlorophyll grain as it becomes fully adult is simply due to the 
increased activity of assimilation (see pp. 453-4), and is not 
in any way related to the disappearance of the red dye, for the 
same phenomenon is shown by leaves which remain red when 
adult, provided assimilation is sufficiently active. Similarly with 
(2), the deposition of starch in young-developing chlorophyll 
grains is in no way related to the presence of a red-colouriug 
material in the cell-sap, and takes place equally well in young 
leaves in which all red colour is absent. In (3) the phenomenon 
is due to the illumination, and hence also the assimilation, being 
weaker than normal. In such cases sugar does not accumulate 
in the palisade parenchyma in suffieient amount to reach the 
starch-forming percentage; but in the mesophyll, especially 
around the veins, owing to the narrowing of the channel 
through which it passes, the sugar accumulates, reaches the 
starch-forming percentage, and starch grains appear in the 
mesophyll cells. 
None of the observations cited by Pick form a certain proof 
that the special importance of the red dye is due to its cutting 
off those rays of light which hinder or prevent the translocation 
of carbohydrates. The function of the red dye seems to be 
mainly to protect the plasma against the photo-chemical action 
of strong sunlight. When the red dye is present, as is often 
the case, over the veins and conducting tissues only, it will, 
as Johow has shown, by virtue of this protective influence aid 
translocation in general. Over the assimilatory portion of the 
leaf, though it appears to exercise a slight protective influence 
against the beating effect of the sun’s rays, and also helps to 
protect the chlorophyll against the decomposition induced by the 
action of sunlight, the main function of the red dye is to protect 
212 
