vii.] ON THE PHYSICAL BASIS OF LIFE. 125 



internal circulation, which has been put forward by an 

 eminent physiologist, loses much of its startling character. 

 Currents similar to those of the hairs of the nettle have 

 been observed in a great multitude of very different 

 plants, and weighty authorities have suggested that they 

 probably occur, in more or less, perfection, in all young 

 vegetable cells. If such be the case, the wonderful 

 noonday silence of a tropical forest is, after all, due only 

 to the dulness of our hearing ; and could our ears catch 

 the murmur of these tiny Maelstroms, as they whirl in 

 the innumerable myriads of living cells which constitute 

 each tree, we should be stunned, as with the roar of 

 a ereat citv. 



Among the lower plants, it is the rule rather than the 

 exception, that contractility should be still more openly 

 manifested at some periods of their existence. The 

 protoplasm of Algce and Fungi becomes, under many 

 circumstances, partially, or completely, freed from its 

 woody case, and exhibits movements of its whole mass, 

 or is propelled by the contractility of one, or more, hair- 

 like prolongations of its body, which are called vibratile 

 cilia. And, so far as the conditions of the manifestation 

 of the phenomena of contractility have yet been studied, 

 they are the same for the plant as for the animal. Heat 

 and electric shocks influence both, and in the same way, 

 though it may be in different degrees. It is by no means 

 my intention to suggest that there is no difference in 

 faculty between the lowest plant and the highest, or 

 between plants and animals. But the difference between 

 the powers of the lowest plant, or animal, and those of 

 the highest, is one of degree, not of kind, and depends, 

 as Milne-Edwards long ago so well pointed out, upon 

 the extent to which the principle of the division of 

 labour is carried out in the living economy. In the 

 lowest organism all parts are competent to perform all 



