288 Mr Philip Sewell on the [sess. ui. 



and ferments mentioned by Vines as resulting in different 

 amount from varying degrees of exposure to light. 



Perhaps the clearest example of the chief indirect effect 

 of lisrht, in which a greater amount of assimilated material 

 increases the brilliance of colour, is afforded by the experi- 

 ment of Flahault upon plants grown at Paris and Upsala ; 

 the increase of colour in plants of the same species grown 

 in the latter place is accountable for by the 170 hours 

 more direct sunlight there in the course of the summer. 



Cut flowers, which contained chlorophyll, were also shown 

 by Flahault to colour very noticeably when placed in water 

 and exposed to light. He corroborated Sachs' statement for 

 a large numlier of plants, though not for all, that " flowers " 

 will colour to their normal brilliance in complete darkness, 

 provided they have a sufficient supply of nutritive material, 

 which may be converted into colouring matter. Certain 

 plants depend for much of their brilliancy on assimilation 

 which takes place in leaves of the same year, and there- 

 fore they do not colour so brightly if their leaves are 

 witldield from light, or injured so as to prevent perfect 

 assimilation. 



(B) Tlic effects of heat in nature are all indirect in a 

 similar way. It affects colour only as it quickens or retards 

 the metabolic processes of growth, as it increases or diminishes 

 the supply of reserve nutritive material in the plant. From 

 this cause may be explained the failure of many flowers 

 to colour brilliantly, or at all, during exceptional or ordinary 

 winters, as has been noticed of the single stock. This 

 will also afford a partial ex])lanation of the asserted pre- 

 valence of white and yellow flowers during winter, if such is 

 prov(;d to be really the case. Cei'tainly it is to an im- 

 poverished nutrition, largely brought about by cliange in 

 temperature, that is due the fact of a cold dam]) winter 

 producing white varieties, or of a droughty summer red 

 varieties. The })rilliant red assumed Ijy many Algic, as, for 

 instance, Palmdbi, OmiMatoria, and Prutococats, according to 

 I'.run, in tlie shallow waters of alpine lakes, is mainly a 

 consc([uen(;e of a higher temperature, which prevents further 

 vegetation, and breaks down or (changes the green material 

 in the ecljs into oth(!r l)rightly coloured ])roducts. 



The more complex condititm of heat with considerable 



