1832.] Scientific Intelligence. 113 



The discovery, by the same gentleman, that essential oil of sassafras will 

 soften caoutchouc so that it may be applied to any surface with a brush, promises 

 also much utility. When dry it becomes again simple caoutchouc, with all its 

 original elasticity ; if it be applied on a plate of glass, dried, and then immersed 

 in cold water, the sheet may be peeled off. It has been spread upon paper, and 

 after becoming dry, the whole immersed in water, when on stretching it, the paper 

 would, of course, separate into fragments, between which the gum elastic might 

 he stretched, so as to separate them to the distance of a quarter of an inch without 

 itself giving way, notwithstanding its tenuity ; such a varnish will never crack, 

 one of its essential attributes being elasticity. 



7. — Directions for collecting and preserving Plants in foreign Countries. By W. J. 



Hooker, LL.D. Reg. Prof. Bot. at Glasgow. 



On preserving Plants for a Hortus Siccus. 



This is a much simpler process than is generally imagined by those unpractised 

 in it; and many travellers have been deterred from collecting specimens by the time 

 and trouble requisite for securing them in the way that has been generally recom- 

 mended. 



The main circumstances to be attended to are, to preserve specimens of plants 

 in such a manner that the moisture may be quickly absorbed, the colours as much 

 as possible preserved, and such a degree of pressure given to them, as that they 

 may not curl up in the act of drying. 



For this purpose, let a quantity of separate sheets of paper be obtained, of a 

 folio size; and of an absorbent nature. Common cartridge or gray paper is per- 

 haps the best. Brown paper does well enough for coarse plants, and blotting 

 paper for the more delicate kinds. Two boards should be provided, one for the 

 top and the other for the bottom of the mass of papers. For pressure at home, or 

 when stationary for any length of time in a given spot, nothing serves better as a 

 press than a weight of any kind, a large stone, a great book, &c. put upon the 

 topmost board ; and the great advantage in this is, that the weight follows the 

 shrinking of the plants beneath. Whilst travelling, nothing is so convenient as 

 three leathern straps with buckles — two to bind the boards transversely, and one 

 longitudinally. It will be farther desirable to have a number of pieces of pasteboard, 

 of the same size as the paper, to separate different portions of the collection, either 

 such as are in a different state of dryness, or such as, by their hard or stout woody 

 nature, might otherwise press upon more delicate ones that are in papers adjoin- 

 ing, and be the means of injuring them. 



Thus provided, gather your specimens : if the plants be small, root and stem ; if 

 large, cut off portions of the branches of a foot or a foot and a half long, selecting 

 always such as are in flower, and others in a more or less advanced state of fruit. 

 Place them side by side, but never one upon another, on the same sheet, and lay 

 upon them one, two, or three sheets, according to the thickness of your paper or 

 of your plants, and so on, layer above layer of paper and specimens, subjecting 

 them then to pressure. As soon as you find that the paper has absorbed a consider- 

 able portion of the moisture, (which will be according to the more or less succu- 

 lent nature of the plants, and the heat and dryness of the season or climate,) 

 remove the specimens into fresh papers ; and let the old papers be dried for use 

 again, either in the open air and sun, or in a heated room, or before the fire. 



As to the spreading out of the leaves and flowers with small weights, penny pieces, 

 &.c. it is quite needless. The leaves and flowers are best displayed by nature in 



