48 VEGETABLE ORGANOGRAPHY. 



affirmed, and from which one must draw an opposite 

 conclusion. Thus it is certain, that the first woody 

 layer of trees contains trachese in a state incapable of 

 unrolling, even in aged stems ; and that they have not 

 been found in the next layers, even in a young state. 



Those who derive the origin of vessels from the cel- 

 lular tissue, support their opinion, 1st, upon this, — that 

 in the vegetable kingdom the cellular tissue is the most 

 universal texture, and that it alone composes those 

 plants which appear the least perfect ; 2d, that in every 

 plant it is more abundant in the individual or its organs 

 at the time of their first development, than at an ad- 

 vanced age. The first of these proofs appears to me to 

 be deduced from an inadmissible description of reason- 

 ing — viz. the plan of considering the vegetable kingdom 

 as an individual plant, and of deciding upon one species 

 and one class from another, as if the general forms of 

 beings were endowed with immutability. As for the 

 second, the point is true ; but it is as easily explained 

 by supposing that the development of vessels is a Httlc 

 slower than that of the cellules. 



Lastly. There is a thii*d class of anatomists who re- 

 gard all the fonns of vessels as constant, and who assert 

 that age does not determine the forms under which the 

 different orders of vessels have been established. But 

 even these give credit to the incrustation of the cellules 

 of the wood and bark, to the formation of an analogous 

 incrustation, or a development of a peculiar cellular tissue 

 in the aged vessels : and it must be confessed that their 

 principal argument is purely negative ; that is to say, 

 that it relies upon the fact, that none of the changes 

 admitted in the different theories have ever been de- 

 monstrated by direct observation. 



4th. What is the nature of the markings which are 

 observed on (he dotted and strangulated vessels? This 



