122 DIFFERENCE IN COLOUR OF FLOWERS AND FOLIAGE. 



that our tropical plants are collected from regions widely 

 separated from each other. 



It would indeed seem that while the tropical regions are 

 far richer in the production of vegetable forms, so far as 

 regards brilliancy of colour we have the advantage ; that is, 

 the vegetation of temperate is more brilliant in hue than 

 that of tropical regions. As probable causes for this state 

 of things in tropical climates may be assigned greater 

 general richness of soil and amoimt of moisture in the air, 

 as opposed to the generally poorer soil and drier atmosphere, 

 together perhaps with the gi-eater amount of sunlight, in 

 temperate regions. In our own climate, for instance, under 

 the conditions of a clear blue sky, plenty of sunlight, a light 

 soil and a dry season, the colour of the flowers is naturally 

 more brilliant than it is under conditions of an opposite 

 character. 



The perhaps greater number of brilliant coloured flowers 

 in our climate may be in part accounted for by the visits 

 of insects to different flowers ; for whenever a flower shows 

 any tendency to vary in the direction of brilliancy of colour, 

 it is probably visited by them, and its propagation ensured 

 by the transmission of the pollen to another plant, the 

 tendency to brilliancy of colour being increased by heredity, 

 and further confirmed by suitable conditions of gi^owth, etc. 

 In connection with this subject, the question suggests itself: 

 Do cultivated plants come under the same law as wild 

 animals in a state of confinement ? 



We know that in some cases wild animals are not so 

 fertile in confinement as when free, and it would seem that 

 a certain degree of change is thus produced in the genera- 

 tive organs inducing partial sterility ; there seem.s also some 

 reason to believe that, as a plant tends to vary, so does it 

 suffer in its fertility. The cultivation of plants often pro- 



