With propolis, bees attach the combs to the roof and sides of their dwelling, stop crevices, fasten the hives or boxes to the floors and roofs, strengthen the weak places of their domicile, and varnish the cell-work of their combs. The chapter on Instincts details the modes in which bees employ it for their protection against intruders into their hives. From its being used for the firm attachment of combs to the roofs of hives, it must be the first matter collected by a recent swarm. The term Propolis is derived from the Greek, and signifies 'before the city,' bees having been observed to make use of it, in strengthening the outworks of their city. Reaumur was unable to discover its vegetable source. It is generally supposed to be gathered from the resinous exudations of the poplar, alder, birch, and willow; according to Riem, from pines and other trees of the fir tribe; though some authors have alleged that bees can produce it where no such trees are near them, and that turpentine and other resins have been disregarded when laid before them. A recent experiment of Huber has solved this question: he planted in spring some branches of the wild poplar, before the leaves were developed, and placed them in pots near his apiary: the bees alighting on them separated the folds of the largest buds with their forceps, extracted the varnish in threads, and loaded with it, first one thigh and then the other; for they convey it like pollen, transferring it by the first pair of legs to the second, by which it is lodged in the hollow of the third. Huber examined the chemical properties of this varnish, and identified it with the propolis which fastens the combs to the hives. With respect to the absence of fir-trees, &c. in the neighbourhood of the hives, it is to be recollected, in the first place, that _bees will fly about three miles_ (some say five,) for what they may want: +Huber+ _thinks that the radius of the circle they traverse does not exceed half a league_, yet says that the question is undecided. In the second place, that a balsamic and tenacious secretion is found upon the buds of several plants and trees, which are often crowded with these insects; such for instance as the tacamahac, horse-chesnut, and hollyhock. Dr. Evans says that he has been an eye-witness of their collecting the balsamic varnish which coats the young blossom buds of the hollyhock, and has seen them rest at least ten minutes on the same bud, moulding the balsam with their fore-feet and transferring it to the hinder legs, as above stated. When finally moulded, the pellets of propolis are of a lenticular form.