ON THE PHYSICAL BASIS OF LIFE 95 



an 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 tropi- 

 cal forest is, after all, due only to the dulness of our hearing; 

 and could our ears catch the murmur of these tiny Mael- 

 stroms, 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 ex- 

 ception, that contractility should be still more openly man- 

 ifested at some periods of their existence. The protoplasm 

 of Alg(E and Fungi becomes, under many circumstances, 

 partially, or completely, freed from its woody case, and ex- 

 hibits 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 contrac- 

 tility 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 

 w^hich 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 



