Page:Makers of British botany.djvu/128

 94 Construction of Timber. In order that other investigators might benefit from his experience he fully described and figured the instruments used; of particular interest is a small hand microtome with which he cut his sections. This ingenious tool was the invention of Cummings, and does not differ in essentials markedly from some the writer has seen in use; Hill claims that when the cutter was particularly sharp sections no thicker than a 2000th part of an inch could be obtained. The microscope was made by Adams under the direction of Hill and his patron, unnamed in the book, but in all probability Lord Bute, and embodied some improvements on earlier instruments. This microscope is figured in Carpenter's work on The Microscope and its Revelations.

The Construction of Timber is well arranged: the work begins with a general description of the tissues and their disposition in a thickened stem; then follows a more detailed account of the separate tissues; and finally much space is devoted to a comparison of different tissues in various plants.

Hill's account is fully illustrated with copper plates; his figures of sections are not highly magnified, some not more than twelve times, and their quality is not equal to the best in Grew's Anatomy.

Hill principally studied transverse sections, and consequently fell into errors which he might have avoided by the careful observation of longitudinal ones; also he used macerated material, but as his method preserved only the stronger walled elements he did not gain to any great extent from their use.

The parts devoted to comparative anatomy are not at all bad, and they give a concrete idea of the differences obtaining in the different plants.

He apparently understood the nature of the annual rings, and of them he wrote as follows: "These are the several coats of Wood, added from season to season. It has been supposed that each circle is the growth of a year; but a careful attention to the encrease of wood has shewn me, beyond a doubt, that two such are formed each year; the one in the Spring, the other soon after Midsummer." His illustration, however, is not so clear as