418 Organization of Plants. 



and moisture, are the essentials required. This is more strikingly- 

 shown in the process of malting than even in the natural condition ; 

 and it is only by the most scrupulous attention to these points that 

 the required change can be produced in the seed. The question 

 whether the luminous or the chemical rays are the most beneficial to 

 the growth of plants, is still open for examination. Dr. Draper 

 states positively, as the result of his enquiries, that the luminous rays 

 alone act in producing the decomposition of carbonic acid by plants, 

 and in forming the colouring matter of the leaves ; whilst the chemi- 

 cal rays are active in producing motion — that is, that the bending of 

 plants towards the light is due to their influence. Upon these points 

 he is at issue with other investigators, who have stated the very 

 reverse of these results. We hope that the question will be set at rest 

 by some careful experiments on both these points. The circulatory 

 system of plants is another point which is brought under consider- 

 ation. The rise and fall of the sap, in obedience to laws regulated 

 by the changes of the seasons, are phenomena upon which there has 

 been much speculation, and some very good experiments. When we 

 consider the force necessary to lift a column of water sixty or seventy 

 feet, we shall perceive that no unimportant power is brought into 

 action in raising the sap to the " topmost twig" of the tallest trees. 

 Capillary attraction has been called in to aid the ascending current ; 

 but this, it has generally been admitted, is an inadequate power. 

 Vital action — a term to which no very definite meaning can be at- 

 tached — is brought to the aid of capillary attraction. With these 

 powers several theoretical writers have been satisfied, and the world 

 has rested somewhat contentedly with an explanation which it could 

 not understand. It is not unfrequent that we are content to hide 

 our ignorance under a sounding epithet. Dutrochet and Porret dis- 

 covered the peculiar power of organized diaphragms in raising water 

 above its natural level. More recent investigations have shown that 

 this power is not confined to organized tissue, but that any porous 

 body, with its two sides in opposite electrical conditions, has the 

 power of endosmose and exosmose to a remarkable extent. The force 

 with which this principle will overcome resistance is exceedingly 

 great. To this action, then, associated with capillary attraction, Dr. 

 Draper is inclined to refer the rise of sap in the vessels of plants. This, 



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