100 ON THE PHYSICAL BASIS OF LIFE 



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

 young vegetable cells. If such be the case, the wonder- 

 ful 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 great city. 



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 Algcs 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 o' 

 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 de- 

 grees. 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 de- 

 gree, 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 functions, and one and the 

 same portion of protoplasm may successfully take on 

 the function of feeding, moving, or reproducing appara- 

 tus. In the highest, on the contrary, a great number of 



