54 VITAL FORCE, INSTINCT, AND SENSATION. 
a central organ in relation to the protoplast that lives in a solitary cell. It is 
not of course to be supposed that within a whole plant-structure, that is in the 
community of live protoplasts which constitutes an individual plant, such a con- 
centration of stimulation could occur as is the case with individual animals which 
have nerve-fibres all converging into the brain; but between the sensation of 
animals without nerves and that of plants no essential difference can exist. 
Hence we infer that there is no barrier between plants and animals. The 
attempt to establish a boundary-line where the realm of plants ceases and the 
animal world begins is a vain one. If we naturalists, all the same, agree to 
separate plants and animals, we do so only because experience shows that a 
division of labour conduces to a speedier attainment of our object. On the 
intermediate ground where animals and plants meet, zoologists and botanists 
encounter one another, not, however, as hostile rivals with a view to exclusive 
possession of the field, but as colleagues with a common interest in the adminis- 
tration and cultivation of this jointly tenanted region. 
