Thorns are of two kinds, Lignous and Cortical. Of the first are such as those of the Hawthorn, and are constituted of all the same substantial Parts whereof the Germen it self, and in a like proportion: which also in their Infancy are set with the resemblances of divers minute Leaves. In affinity with these are the Spinets or Thorny Prickles upon the Verges and Tops of divers Leaves, as of Barberry, Holly, Thistle, Furze, and others; all which I think are the filamentous extremities of the Lignous Body sheathed in the Skin.
Cortical Thorns are such as those of the Rasberry Bush, being not, unless in a most extraordinary small proportion propagated from the Lignous Body, but almost wholly from the Cortical and Skin, or from the Barque.
The growth of this Thorn may farther argue what in [the Second Chapter] we supposed; sc. That as the proper tendency of the Lignous Body, is to ascend, so of the Cortical to descend. For as the Lignous Thorn, like other Parts upon the Trunk, in its growth ascends; this being almost wholly Cortical, pointeth downward. The use of Thorns the very Ingenious Mr. Sharrock observed.
Upon the Leaves of divers Plants two Productions shew themselves, sc. Hairs and Globulets. Of Hairs, only one kind is taken notice of, although they are various. Ordinarily they are plain; which when fine and thick set, as on most Hairy Buds; or fine and long, as on those of the Vine, we call them Down.
But sometimes they are not plain, but branched out, from the bottom to the top, reciprocally on every side, in some resemblance to a Stags-Horn; as in Mullen. And sometimes they are Astral, as upon Lavender, and some other Leaves, and especially those of Wild Olive; wherein every Hair rising in one round entire Basis a little way above the Surface of the Leaf, is then disparted. Star-like, into several, four, five or six points, all standing at right Angles with the said perpendicular Basis.
The Uses of Hairs are for Distinction and Protection. That of Distinction is but secondary, the Leaves being grown to a considerable size. That of Protection is the prime, for which they were originally form’d together with the Leaves themselves, and whose service they enjoy in their Infant-estate: For the Hairs being then in form of a Down, alwayes very thick set, thus give that protection to the Leaves, which their exceeding tenderness then requires; so that they seem to be vested with a Coat of Frieze, or to be kept warm, like young and dainty Chickens, in Wooll.
Globulets are seen upon Orach, both Garden and wild; and yet more plainly on Mercury or Bonus Henricus. In these, growing almost upon the whole Plant, and being very large, they are by all taken notice of.
But strict Observation discovers, that these Globulets are the natural and constant Off-spring of very many other Plants. Both these Globulets, and likewise the diversity of Hairs, I find the Learned Mr. Hook hath already observed. They are of two kinds; Transparent, as upon the Leaves of Hysop, Mint, Baume, and many more: White, as upon those of Germander, Sage, and others. All which, though the naked Eye will discover, yet by the help of Glasses we may observe most distinctly. The use of these we suppose the same with those of the Flower, whereof we shall speak.