Miscellaneous. 337 



and in these cases it is self-evident that sunlight is a cause of colour. 

 Yet if we pluck such a variety from the tree, and place it in the 

 sunlight, it will not colour; so that we see here that there must be 

 a connexion with the living principle in the tree to enable the solar 

 ravs to act. Yet it requires a relaxation of the leaf's hold on life 

 to bring out these colours. At any time during the summer a 

 maturing leaf on an American tree exhil)its bright colour ; yet if a 

 dying leaf, half-coloured, be plucked from the parent stem, there is 

 no further change in the tint. Many leaves pass through grades, as 

 green, light yellow, orange-brown to scarlet. If they are gathered 

 ab yellow or brown they remain yellow or brown, and so on all 

 through these stages. Colouring, therefore, could not wholly be 

 considered chemically ; for though decay, which we take to be a 

 chemical action, is going on during the colouring stage, complete 

 separation from the living tree at once stops the process. 



If we consider these two facts together, and then some other 

 known natural laws, we may form some reasonable hypothesis. 

 There is, for instance, the principle of heredity, so ably insisted on 

 by Mr. Darwin, in connexion with all living tilings. A force once 

 applied to an object exerts an influence after the power has been 

 removed. A wheel runs round after the hand which turns it is 

 taken away ; and a change in a plant brought about by any cir- 

 cumstance will continue in connexion with that plant some gone- 

 rations after the circumstances have ceased to exist. That this is 

 BO has been proved by iS'audin with hybrid (or perhaps we should 

 say crossed) lettuces, and in other ways. Supposing, then, these 

 closely allied species to have been originally of one parentage, how 

 did the power in one case to change to bright colour, or in the 

 other to resist the tendency to colour, originate ? If by chemical 

 power alone, it would occur at once, as a piece of white wood is at 

 once browned by fire ; but with the vital principle opposed to this 

 chemically destructive principle, it would take moi'e time to accom- 

 plish this change, and, the change once made, would again require 

 more time to again alter the fixed condition. This is essentially the 

 foundation of the law of heredity; and under its operation we could 

 not reasonably look for a change in the colouring-power of these 

 European trees, although light were an active agent, under even 

 more than five or ten inheriting generations. 



At any rate we have in these salt-marsh plants the evidence that 

 the plants of one country, in that country colourlt^ss, can be made to 

 take the most brilliant colours when growing in ours. That these 

 plants had one primary origin is certain, though the ancestry may 

 have been separated by thousands of years. We know that 'plants 

 introduced at once do not change at once ; heredity forbids it. We 

 may assume, therefore, that it was only after some generations on 

 the American coast, under the influence perhaps of American li"ht 

 that these European plants showed their American colours. We can 

 see in these annual plants, with a new generation every vear, the 

 results in numerous generations, as we cannot see in the more slowly 

 reproducing tree. 



