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dependent on its agency. It cannot indeed be assumed 

 that plants will not continue to grow, unless they are 

 supplied with an intense degree of light ; but it is certain 

 that the successful nature of their growth, their matura- 

 tion, and their fructification, are dependent in no ordi- 

 nary degree upon the nature and force of its action ; for 

 without it, the vital energies of animated beings are un- 

 able to maintain and perform the processes of elaboration, 

 and assimilation, upon which their nutrition depends. 

 The mere extension of vegetable tissue, may indeed go 

 on, though less satisfactorily, under the almost total pri- 

 vation of light, but with the exception of cryptogamic 

 vegetation, the organs of fructification are not under 

 those circumstances, produced at all : the stem may be 

 formed, but does not become solid : the leaves may ex- 

 pand, but their condition is imperfect ; and it is only by 

 means of the full and complete action of these organs in 

 the nutrition of plants, that the developement of the 

 floral parts is brought about: the roots may take up 

 fluids, and these may be conveyed in the natural upward 

 channels, and then dispersed among the stems and the 

 leaves ; but it is the action of solar light, aided indeed by 

 the natural condition of the elements supplying heat and 

 moisture, which alone, by a process of elaboration, can 

 convert this fluid, once crude and undigested, into the 

 compound organic substances, such as lignin, gum, 

 starch, gluten, &c. which in their turn, are destined to 

 minister to the support of the organs of reproduction. 

 Growth, that is mere extension, may go on in proportion 

 as heat and moisture are supplied to plants, but light is 

 the agent to whose especial influence we owe the pro- 

 duction of their active properties and secretions, and the 

 perfection of their fruit. 



If then light is so indispensable to the vegetable frame, 

 how important it is that the structures which we devote 

 to the cultivation of such plants as the Cucumber, which 



