68 
enable the philosophical agriculturist to understand 
the functions of plants ; those who wish to study 
the anatomy of vegetables, as a distinct science, 
will find abundant materials in the works of the 
authors I have quoted, page 9., and likewise in the 
writings of Linnaeus, Desfontaines, Decandolle, 
De Saussure, Bonnet, and Smith. 
The history of the peculiarities of structure in 
the different vegetable classes rather belongs to 
botanical than agricultural knowledge. As I 
mentioned in the commencement of this Lecture, 
their organs are possessed of the most distinct 
analogies, and are governed by the same laws. In 
the grasses and palms, the cortical layers are 
larger in proportion than the other parts ; but their 
uses seem to be the same as in forest trees. 
In bulbous roots, the alburnous substance forms 
the largest part of the vegetable ; but in all cases 
it seems to contain the sap, or solid materials de- 
posited from the sap. 
The slender and comparatively dry leaves of the 
pine and the cedar perform the same functions as 
the large and juicy leaves of the fig-tree, or the 
walnut. 
Even in the cryptogamia class, where no flowers 
are distinct, still there is every reason to believe 
that the production of the seed is effected in the 
same way as in the more perfect plants. The 
mosses and lichens, which belong to this family, 
have no distinct leaves, or roots, but they are 
furnished with filaments which perform the same 
functions ; and even in the fungus and the mush- 
room there is a system for the absorption and aera- 
tion of the sap. 
