40 THE FLORIST. 



have been the case ; all analogy is against such a theory. The peculiar 

 constitution of plants, as well as of the atmosphere, niust have been 

 different; and experiments made to show whether plants could de- 

 compose a larger amount of carbonic acid, if the atmosphere contained 

 it, infirm us that such is not the case. We must therefore refer the 

 peculiar vegetation of that period toclimatal intiuences, favoured perhaps 

 with a tropical sun and abundance of light ; for we can hardly reconcile 

 the close approach to tropical forms, among the Flora of the. coal period, 

 with a climate similar to what exists on the same spot at the present. 

 Passing onwards, we find, subsequently, remains of vegetation differing 

 from those of the period just noticed, and by degrees approximating in 

 form and character towards those of the present time. 



This short epitome of vegetable history I have thought necessary, to 

 connect tlie chain of evidence in respect t ) the influence that light has 

 exercised, through all time, in changing and modifying the aspect of 

 external nature. 



That light has great influence in deciding the colour of both plants 

 and animals, is well known. In tropical climates, under the effects of 

 a brilliant sun, vegetation assumes her darkest and ricliest green ; 

 flowers and fruits are tinged with colours of the deepest dye. In tem- 

 perate climates, plants present a more subdued colour, and we miss the 

 gaudy colours of the flowers of tropical regions : while, farther north, 

 there is but little colour in the flowers, and the subdued forms of vegetable 

 life show how much they miss the invigorating stimulant of light. So 

 it is with plants cultivated under glass, freely exposed to even the light 

 of an English climate ; they will show, by the greenness of their foliage 

 and bright colour of their flowers, how congenial light is to their welfare: 

 on the other hand, when grown in- dark, badly -constructed houses, 

 the sickly foliage and drawn-up stems show the want of this necessary 

 element. I shall, however, reserve what I have to say on this to the 

 conclusion of my paper. 



The green colour in plants is dependent on the presence of a peculiar 

 matter formed in the leaves of plants, called chlorophylle, and which is 

 the result of the action of the sun's rays on the leaves. This chloro- 

 phylle is a carbonaceous compound, and no doubt it serves important 

 purposes in the process of assimilation. The sun's rays, as they fall on 

 the surface of the earth, possess very different properties, and these may 

 be separated, so as to be made to act independently of each other. 

 These properties and principles are represented by the red, yellow, and 

 blue colours of the prismatic spectrum, and which respectively represent 

 the caloric or heating rays, the luminous rays, and the actinic or 

 chemical rays ; each, as I shall show hereafter, have theii- allotted 

 sphere of duty in reference to promoting vegetation. 



The influence of light on vegetation, in promoting the decomposition 

 of carbonic acid, contained at all times in atmospheric air, is well known, 

 and will be noticed more at length hereafter, as I purpose ending this 

 paper by again adverting to the influences of the three principles found 

 in the sun's rays on vegetation. 



Writers on the subject inform us, that the actinic or chemical rays 



