This substance is obtained by the bees from the resinous buds and limbs of trees; and when first gathered, it is usually of a bright golden color, and is exceedingly sticky. The different kinds of poplars furnish a rich supply. The bees bring it on their thighs just as they do bee bread; and I have caught them as they were entering with a load, and taken it from them. It adheres so firmly that it is difficult to remove it. "Huber 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." The smell of the propolis is often precisely similar to that of the resin from the poplar, and chemical analysis proves the identity of the two substances. It is frequently gathered from the alder, horse-chestnut, birch, and willow; and as some think, from pines and other trees of the fir kind. I have often known bees to enter the shops where varnishing was being carried on, attracted evidently by the smell: and Bevan mentions the fact of their carrying off a composition of wax and turpentine, from trees to which it had been applied. Dr. Evans says that he has seen them collect the balsamic varnish which coats the young blossom buds of the hollyhock, and has known them to rest at least ten minutes on the same bud, moulding the balsam with their fore feet, and transferring it to the hinder legs, as described by Huber. "With merry hum the Willow's copse they scale, The Fir's dark pyramid, or Poplar pale, Scoop from the Aider's leaf its oozy flood, Or strip the Chestnut's resin-coated bud, Skim the light tear that tips Narcissus' ray, Or round the Hollyhock's hoar fragrance play. Soon temper'd to their will through eve's low beam, And link'd in airy bands the viscous stream, They waft their nut-brown loads exulting home, That form a fret-work for the future comb; Caulk every chink where rushing winds may roar, And seal their circling ramparts to the floor." _Evans._ A mixture of wax and propolis is used by the bees to strengthen the attachments of the combs to the top and sides of the hive, and serves most admirably for this purpose, as it is much more adhesive than wax alone. If the combs, as soon as they are built, are not filled with honey or brood, they are beautifully varnished with a most delicate coating of this material, which adds exceedingly to their strength: but as this natural varnish impairs their delicate whiteness, they ought not to be allowed to remain in the surplus honey receptacles, accessible to the bees, unless when they are actively engaged in storing them with honey.