Mica, talc, chlorite, haematite), or in long blades or fibres (anthophyllite, tremolite, actinolite, tourmaline), and, when these have a well marked parallel arrangement in definite bands or folia, the rock will break far more easily along the bands than across them.
Across the folia have been found, and rectangular sheets measuring 30 by 24 in.
Besides those already mentioned, his works include An Outline of the First Principles of Horticulture (1832), An Outline of the Structure and Physiology of Plants (1832), A Natural System of Botany (1836), The Fossil Flora of Great Britain (with William Hutton, 1831-1837), Flora Medica (1838), Theory of Horticulture (1840), The Vegetable Kingdom (1846), Folia Orchidacea (1852), Descriptive Botany (1858).
The leaves of the foxglove, gathered from wild plants when about two-thirds of their flowers are expanded, deprived usually of the petiole and the thicker part of the midrib, and dried, constitute the drug digitalis or digitalis folia of the Pharmacopoeia.
So, too, his great work on penance gave equal offence to the Jesuits and to Port-Royal, and even after his death, in 1659, the polemical vehemence of his Exercitationes biblicae, and the exaggeration of his assertion "apud neotericos Haereticos verba Scripturarum non esse integra, non superficiem, non folia, nedum sensum, medullam et radicem rationis" long led Protestants to treat his valuable contributions to the history of the Hebrew text as a mere utterance of Popish prejudice.