LIGHT, AS A CONDITION OF VITAL ACTIVITY. 61 



4 



early condition of the higher organisms ; their embryos, like those 

 beings of permanently-low type which they resemble in degree of deve- 

 lopment, being liable to be affected by modifying causes, which the 

 perfect beings of the same kind are able to resist. It is. in this way 

 that we are to explain the influence which the female parent exerts 

 upon the embryo, during the period through which it is dependent upon 

 her for the materials for its development. 



1. Of Light, as a Condition of Vital Activity. 



79. The importance of this agent, not only to the Vegetable but to 

 the Animal World, is not in general sufficiently estimated. Under its 

 influence alone can that first process be accomplished, by which Inor- 

 ganic matter is transformed into an Organic compound, adapted by its 

 nature and properties to form part of the organized fabric. The fol- 

 lowing is an example of the simplest phenomenon of this kind ; and it 

 demonstrates the influence of Light the more clearly on account of that 

 simplicity. " If we expose some spring-water to the sunshine, though 

 it may have been clear and transparent at first, it presently begins to 

 assume a greenish tint ; and, after a while, flocks of green matter col- 

 lect on the sides of the vessel in which it is contained. On these flocks, 

 whenever the sun is shining, bubbles of gas may be seen, which, if col- 

 lected, prove to be a mixture of oxygen and nitrogen, the proportion 

 of the two being variable. Meanwhile the green matter rapidly grows ; 

 its new parts, as they are developed, being all day long covered with 

 air-bells, which disappear as soon as the sun has set. If these observa- 

 tions be made upon a stream of water, the current of which runs slowly, 

 it will be discovered that the green matter serves as food for thousands 

 of aquatic Insects, which make their habitations in it. These insects 

 are endowed with powers of rapid locomotion, and possess a highly- 

 organized structure ; in their turn they fall a prey to the Fishes which 

 frequent such streams."* Such is the general succession of nutritive 

 actions in the Organized Creation. The highest Animal is either 

 directly dependent upon the Vegetable Kingdom for the materials of 

 its fabric, or it is furnished with these by some other Animal, this again 

 (it may be) by another, and so on ; the last in the series being always 

 necessitated to find its support in the Vegetable kingdom, since the 

 Animal does not possess the power of causing the Inorganic elements 

 to unite into even the simplest Organic compound. This power is pos- 

 sessed in a high degree by Plants ; but it can only be exercised under 

 the influence of Light. We shall now examine, more in detail, the 

 conditions of this influence, both in the instance just quoted, and in 

 others drawn from the actions of the higher Vegetable organisms. 



The "green matter of Priestley," (as it is commonly called), 

 which makes its appearance when water of average purity is submitted 

 to the action of the Sun's light, and which also presents itself on the 

 surface of walls and rocks that are constantly kept damp, is now known 

 by Botanists to consist of cells in various stages of development, the 



* Prof. Draper, on the Forces which produce the Organization of Plants ; p. 15. 



