208 THE INDUCTIONS OF BIOLOGY. 



commercial travellers, though having in one sense a 

 separate occupation, have in another sense an occupation 

 forming part of each of the many occupations which it 

 aids. As it is here with the sociological division of 



labour, so is it with the physiological division of labour 

 above described. Just as we see in an advanced community, 

 that while the magisterial, the clerical, the medical, the legal, 

 the manufacturing, and the commercial activities, have grown 

 distinct, they have yet their agencies mingled together in 

 every locality; so in a developed organism, we see that while 

 the general functions of circulation, secretion, absorption, 

 excretion, contraction, excitation, &c., have become differ- 

 entiated, yet through the ramifications of the systems appor- 

 tioned to them, they are closely combined with one another 

 in every organ. 



60. The physiological division of labour is usually not 

 carried so far as wholly to destroy the primary physiological 

 community of labour. As in societies the adaptation of special 

 classes to special duties, does not entirely disable these classes 

 from performing one another's duties on an emergency ; so in 

 organisms, tissues and structures that have become fitted to 

 the particular offices they have ordinarily to discharge, often 

 remain partially able to discharge other offices. It has been 

 pointed out by Dr. Carpenter, that " in cases where the dif- 

 ferent functions are highly specialized, the general structure 

 retains, more or less, the primitive community of function 

 which originally characterized it." A few instances will 

 bring home this generalization. 



The roots and leaves of plants are widely differentiated in 

 their functions : by the roots, water and mineral substances 

 are absorbed; while the leaves take in, and decompose, car- 

 bonic acid. Nevertheless, by many botanists it is held that 

 some leaves, or parts of them, can absorb water; and in what 

 are popularly called " air-plants," or at any rate in some 

 kinds of them, the absorption of water is mainly and in 



