Essays on the Microscope / Containing a Practical Description of the Most Improved Microscopes, a General History of Insects, etc., etc.

by George Adams

OF THE BLEA.

This is that part of the tree which is formed into wood, and therefore lies between it and the bark, and may be separated from them by maceration.

A longitudinal piece of the blea, when examined by the microscope, exhibits a number of vessels running parallel to each other, the interstitial spaces being filled with a floccose, white, formless substance, of which Dr. Hill suspects even the vessels themselves to be formed. Innumerable small openings or mouths may be discovered in these vessels, suited to imbibe the moisture which is so essential to the life and health of plants. These mouths cannot be well discerned, except when they are opened by the season of the year, either before the first leaves of spring, or in the midsummer shooting time; though a small quantity of moisture will keep them open at that time, yet no quantity would be sufficient at an improper season.[136]

[136] Hill’s Construction of Timber, p. 47.

The blea is a zone more or less perfect, which lies under the bark, and covers or surrounds the wood, and is principally distinguished from it by being less dense. In some species the difference between the blea and the wood is very remarkable, in others it is less so.

The ancient botanists, struck with the difference they observed between the wood and the blea, compared this substance to the fat in animals. Malpighi, Grew, and Du Hamel considered it as the wood not yet arrived to a state of perfection. It is organized in a manner similar to the wood, and possessing the same vessels disposed nearly in the same manner. The juice vessels of this part may be separated from it by maceration; Dr. Hill says, that in this state they appear perfect cylinders, with thick white coats, the surface perfectly uniform.