BRAND, or BURN, a disease in vegetables by which their leaves and tender bark are partially destroyed as if they had been burnt ; hence the name of this disease, which is called Brillure in French. It has been observed that after the leaves have been wetted by dews or gentle rains so that drops adhere to them, and a bright sunshine has succeeded, every spot to which the water had adhered lost its natural colour, and became of a dark or yellow hue ; and on closer examination it was found that the organisation had been partly destroyed, and that these spots no longer possessed the power inherent in healthy leaves of exhaling the water which circulates through them. When this disease is extensive, and attacks the bark as well as the leaves, it frequently causes the death of the plant, and at all events enfeebles its growth and prevents its perfect fructification. The cause of this, like that of most diseases which are common to plants, has been vulgarly ascribed to some unknown atmospheric influence ; and various guesses have been made, which for the most part have little or no foundation. That which appeared most plausible was, that the drops of water being apparently globular, collected the light of the sun into a focus, and produced a sufficient degree of concentration of the calorific rays to burn the tender substance of the leaves. A little reflection will soon convince us that this will not bear examination. The drops which adhere to the leaves and the bark are not globes, but at best flattened hemispheres, and consequently cannot collect the rays of the sun into a focus on the surface to which they adhere ; besides, the spots are as large as the diameter of the drops, ao that all the surface that has been covered with water is injured ; whereas the focus of a globe, such as would actually burn the leaf, must be very small in proportion to the lens which concentrated the rays. It is
mud' more probable that the effect of the water on the tender epider mis of the leaf or bark to which it adheres is similar to that which it has on vegetable matter infused in it ; it softens and dissolves a portion of it, especially when the temperature is somewhat raised, and destroys the vitality. (Do Candolle,' Physiologie V6g6tale.) It is a fact that the principal mischief arises from a sudden .change of temperature soon after sunrise, especially when there has been a heavy dew or hoar-frost in the night ; and careful gardeners brush off the drops from their delicate plants before sunrise to guard against the Brand. Every drop which falls on the leaves of tender plants from the glass which covers a hotbed in which they grow produces a disease exactly similar to that which we have been describing ; and although the vapour of fermenting dung has a pungent ammoniacal smell, it will be found that the water condensed on the glass is nearly pure, and can have no peculiar corroding effect. It acts therefore simply as a dissolvent, and by stopping the evaporation, which is always rapid from the leaves of plants in a hotbed, produces a derange ment in their functions, and ultimately disease.