PHYSIOLOGY. 9299 
fn this respect, therefore, plants likewise resemble 
animals, as in the animal, juices are secreted of very 
different properties, taste and smell. In both king- 
doms, however, the manner in which this is done 
has not yet been explained by physiologists. That 
the secretion and assimilation of the different fluids 
depends on the vital power is certain, but whether 
the attraction of the minute particles, or their mere 
form and shape deserve most attention, is not yet 
known. In the old vessels the irritability is less 
than in young ones, in the last therefore more earthy 
particles are deposited, the sap is sooner concreted, 
and, as they grow in years, they become harder and 
harder. Hence it is that these inner vascular circles 
grow more dense, and form the wood (§ 261). 
‘Those trees i which most carbon is fixed, ac- 
quire a harder wood, and will therefore grow slower 
than others. Some species of beech, Carpinus be- 
tulus, and Fagus sylvatica; the oak tree, Quercus 
robur and pedunculata; the Pinus cedrus, Adansonia 
digitata, and other trees, will serve as instances. But 
even here we have some exceptions ; I will only men- 
tion the Robinia pseudacacia, which fixes a great deal 
of carbon, and in a short time has very hard wood. 
Each organized body, whether animal or plant, 
has been endowed by nature with a peculiar degree 
of vital power, which we cannot estimate, and its 
organization is such, that by an equal supply of 
food, each makes different combinations, depending 
on this unknown power. 
{In a plant, therefore, vegetation goes on according 
to the modifications of the vital power, in the fol- 
Jowing 
