206 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



synthesized provide the proximate starting point for those vastly 

 compHcated chemical operations which result in the formation of new 

 life, and all that that may mean. But not the least wonderful part 

 of the whole process lies in the small amount of carbon dioxide ordin- 

 arily available in the air — only some 2J-3 parts in 10,000 parts of air. 

 The plant could use more, and, if supplied with it, is stimulated to 

 increase the amount of chlorophyll granules — the special m.achinery 

 of the cell more directly concerned with the process. Indeed, 

 provided the light is proportionately increased, the plant is com- 

 petent to utilize more and more carbon dioxide, until other reactions 

 are set agog which progressively interfere with the process and finally 

 arrest its progress. 



Passing over these matters, we may, however, proceed to glance, 

 in the light of what has been said, at one problem which is of practical 

 importance to fruit-growers. I refer to the colouring of apples and 

 such like fruit. We all know that there exists a considerable divergence 

 of opinion amongst practical men as to what condition or conditions 

 are of importance in promoting this colouring. We know that the 

 colouring matter belongs to the class of complex bodies known as 

 anthocyans, and we also know that many plants, e.g. certain sorts of 

 apples, produce them in the outer cells of the skin of the fruit, just as 

 some other plants form them in their leaves, or in the petals, &c., of 

 their flowers. One, amongst others, of the conditions that lead to 

 the formation of these colours appears to depend upon the presence of 

 a relative excess of sugary substances in the cell sap, and therefore 

 anything that will tend to lead to an abnormal accumulation of 

 dissolved sugar may also be expected to result in the appearance of 

 colour. 



It is easy to bring about the presence and the disappearance of a 

 red colour in the leaves of some plants, e.g. of the water frogbit. All 

 that is necessary is to expose the floating plants to bright sun- 

 light at a low temperature. What happens is that the leaf cells under 

 these conditions accumulate a relatively large quantity of sugar 

 instead of turning the excess of it into insoluble starch. This dissolved 

 sugar, which cannot be readily got rid of, begins to react with other 

 substances in the cell, and one of the products thus formed is that 

 which gives the red colour to the leaves. Under ordinary conditions 

 of higher temperature this does not occur, because other chemical 

 processes go on within the cell, leading to the formation of starch 

 at the expense of the sugar. The latter thus does not become suffi- 

 ciently concentrated to initiate the alternative reactions which lead 

 to the production of colour. The chemical process thus outlined is 

 reversible, and the red disappears if the plants are grown on at a higher 

 temperature. Now it is apparently true that the apple is not so 

 simple as the instance to which I have just referred. But that it 

 belongs to the same order I have very little doubt. Complications are 

 introduced by the conditions imposed by the bulky nature of the 

 succulent fruit, and very likely also by the nutritive conditions present 



