HORTICULTURAL JOURNAL. 183 
assume every variety of hue ascribed to the action of the same agents on 
chromule. 
The outward circumstances which tend to change the color of vegetable 
organs are various. The action of light is one of the most efficient agents 
in the production and change of colors, and it is not a little singular that 
the power which is absolutely necessary to the production of color, in the 
great majority of cases, should be the most powerful agent in destroying 
it. We are all acquainted with the infiuence of light in blanching vegetable 
substances when dead. 
The change of the color of leaves in autumn, of fruit when ripening, of 
some evergreen leaves during the winter, are phenomena whose explanation 
has as yet baffled the most acute observers. The memoir of Mohl, above 
quoted, leads us one step further than had before been taken in the expla- 
nation of these common phenomena. 
We can only give in few words the results to which his extended obser- 
vations have led him. He concludes that these various changes are owing 
to a derangement or suspension of functions of the organs of nutrition. 
This point he strengthens by the consideration that the puncture of an 
insect will cause an organ to pass through all the steps to maturity, giving 
all the hues belonging to its species, whether of fruit or leaves. Also, the 
cold of autumn and winter produces a similar derangement ; although the 
agent is different, yet the result is the same. Many evergreen leaves 
become tinged with red in winter from the influence of cold, but, with the 
return of summer, assume their accustomed greenness ; also, the leaves 
of the extremities of the branches being most exposed to atmospheric 
influences are changed to red, while those nearer the trunk continue green. 
If one half of a leaf be protected from the cold it will remain green, while 
the other half will change to red. But in the case of fruit, heat is the 
agent in producing similar effects to those above ascribed to mechanical 
injury and cold. 
Much of the importance attached to flowers by people generally, is 
owing to the orders they exhale. The rose has long been cultivated by 
amateurs, no less for its grateful fragrance, than for its beauties of form 
and color ; and those which combine these properties, are the most favored 
objects of the florist's care. The cause of the odors of plants, is, no 
doubt, the disengagement of a volatile oil, which, in some cases, is easily 
obtained, and made subservient to the use of man ; in others it entirely 
eludes every effort to confine or preserve it, being as evanescent as the 
light, which is the agent of its production. 
