18 PEOPAGAXIOW OF PLANTS. 



as it may be termerl, take^ place when the living tissues 

 of any two closely allied plants are placed in contact, as 

 in the common operations of budding and grafting, for 

 it will seldom occur that the density of the fluids in both 

 stock and cion, or even a bud, will be exactly the same; 

 consequently, a movement, however feeble at first, must 

 follow close contact of the living plant-cells. In soma 

 instances, as I shall have occasion to show in a succeeding 

 chapter, the greater the difference in density of the 

 fluids, the more likely are the two parts to unite quickly 

 and permanently. But it is not to be supposed that the 

 transmission of fluids from cell to cell is all that is neces- 

 sary to make those of one plant support another, or to 

 insure a union between the severed parts of two species 

 or varieties, as in the operations of budding and grafting, 

 for there is an individuality of plants not always easily 

 recognized; still, it exists, and while the transudation of 

 fluids may take place, there must also exist an aflBnity be- 

 tween stock and cion to insure the coalescing of cells. 

 The principle involved cannot, with our present knowl- 

 edge of life in plants, be fully explained, and vegetable 

 physiologists usually refer to the movement of fluids in 

 plants as a mechanical process, probably because this is 

 the easiest way of bridging a chasm that they cannot 

 fathom. The sap of the Oak may flow into a cion from 

 a Hickory by the process of transudation, but the cells of 

 the latter refuse to use it, or even respond to a stimulus 

 from such a source. This individuality in the functions 

 of cells enables one part of a plant to be engaged in ac- 

 cumulating very different elements from those of other 

 parts. The leaves, flowers, roots and bark may all be 

 manufacturing, as it were, quite different substances. 

 The petals of the Kose emit a different scent from that of 

 the leaf or other part of the plant, and that this fra- 

 grance is a distinct product of their cells is shown in 

 the attar of Boses distilled therefrom. Then again 



