PARASITIC GROWTH OP THE MISSELTOE. 205 



adaptation, the Misseltoe, which, from the want of power to 

 form perfect roots, would otherwise be unable to exist, is en- 

 dowed with a compensating power ; it being as much a part of 

 its natural habits to grow upon the stem and branches of trees, 

 as it is for other plants to send their roots down into the ground. 



322. The fibres of the Misseltoe seem to incorporate them- 

 selves completely with those of the stock ; and so intimate is the 

 connection between them, that coloured fluids will pass from the 

 stem into this natural graft, for so it may be termed. It does 

 not appear, however, that any communication exists between 

 the parasite and the bark beneath it, which is always found to 

 be in a dead state around its insertion. But if the part of the 

 branch at which it penetrates be divided with a saw, it will be 

 seen that the two woods are so thoroughly united, that the line 

 of separation between them can scarcely be traced. That the 

 Misseltoe is itself quite deficient in the power of absorbing fluid, 

 has been clearly proved by experiment. If the stem of this 

 plant be cut off and immersed in water, it will absorb little or 

 none of the fluid ; whilst, if a portion of the branch with which 

 it is connected be cut off and immersed in a similar manner, it 

 will absorb nearly as much as if furnished with leaves of its 

 own. 



323. A curious fact illustrative of the great difference in the 

 characters of the ascending and descending sap, is that the former 

 is nearly or quite harmless in those plants whose proper juices 

 have the most virulent properties. Thus, the inhabitants of the 

 Canary islands draw off the former, which serves as a refreshing 

 drink, from the interior of the stem of the Euphorbia canariensis; 

 a tree of which the descending sap is of a very acrid nature, 

 resembling that of the common Spurge of this country, but much 

 more powerful. 



324. The conversion of the water and carbonic acid absorbed 

 by the roots into gum or sugar, involves the setting free a por- 

 tion of the oxygen contained in those compounds ; for as water 

 is composed of oxygen and hydrogen, and carbonic acid of oxygen 

 and carbon, it is evident that, in the production of any substances 

 containing no very large proportion of oxygen combined with 



