1838] 



FA R M E R S ' REGISTER. 



593 





14 



eimilar lo it. The analogy of nature is constant 

 and uniform, and similar effecis are usually pro- 

 duced by similar organs. 



The pith occupies the centre of the wood; its 

 texture is membranous; it is composed of cells, 

 which are circular towards the extremity, and 

 hexagonal in the centre of the substance. In the 

 first infancy of the vegetable, the pith occupies 

 but a small space. It gradually dilates, and in 

 annual shoots and young trees offers a considera- 

 ble diameter. In the more advanced age of the 

 tree, acted on by the heart- wood, pressed by the 

 new layers of the alburnum, it begins to diminish, 

 and in very old forest trees becomes almost imper- 

 ceptible. 



Many different opinions have prevailed with re- 

 gard to the use of the pith. Dr. Hales supposed 

 that it was the great cause of the expansion and 

 developement of the other parts of the plant; that 

 being the most interior, it was likewise the mo.^l 

 acted upon of all the organs, and that from its re- 

 action the phenomena of their developement an'l 

 growth resulted. 

 Vol. VI.— 75 



Linnseus, whose lively imagination was continu- 

 ally employed in endeavors to discover analogies 

 between the animal and vegetable systems, c'on- 

 ceived '-that the pith performed for the plant the 

 same functions as the brain and nerves in ani- 

 mated bemgs." He considered it as the organ of 

 irritability, and the seat of life. 



The latest discoveries have proved that these 

 two opinions are equally erroneous. Mr. Knight 

 has removed the pith in several young trees, and 

 they continued to live and to increase." 



It is evidently, then, only an organ of seconda- 

 ry importance. In early shoots, in vigorous 

 growth, it is filled with moisture; and it is a reser- 

 voir, perhaps, of fluid nourishment at the time it 

 is most wanted. As the heart-wood forms, it is 

 more and more separated from the living part, the 

 alburnum; its functions become extinct, it dimi- 

 nishes, dies, and at last disa[)pears. 



The tendrils, the spines, and other similar parts 

 of plants, are analogous in their organization to 

 the branches, and offer a similar cortical and al- 

 burnous organization. It has been shown, by the 



