258 



SCIENCE OF AGRICULTURE. 



Part II. 



are among the phenomena which have been attributed to instinct. Keith has endeavoured 

 (^Lin. Trans, xi. p. 11.) to establish the doctrine of the existence and agency of an 

 instinctive principle in the plant, upon the ground of the direction invariably assumed by 

 the radicle and plumelet respectively, in the germination of the seed. 



1670. Definition of the plant. But if vegetables are living beings endowed with 

 sensation and instinct, or any thing approaching to it, so as to give them a resemblance 

 to animals, how are we certainly to distinguish the plant from the animal ? At the 

 extremes of the two kingdoms the distinction is easy ; the more perfect animals can never 

 bo mistaken for plants, nor the more perfect plants for animals ; but at the mean, where 

 the two kingdoms may be supposed to unite, the shades of discrimination are so very faint 

 or evanescent that of some individual productions it is almost impossible to say to which 

 of the kingdoms they belong. Hence it is that substances which have at one time been 

 classed among plants, have at another time been classed among animals ; and there are 

 substances to be met with whose place has not yet been satisfactorily determined. Of 

 these may be mentioned the genus Corallina (Jig. 199.), which Linnaeus placed among 



199 



animals, but which Gaertner places among plants. Linnaeus, Bonnet, Hedwig, Mirbel, 

 and Link, have each given particular definitions. According to Link, a plant is a com- 

 pound organic body, deriving nourishment from the soil in which it grows. According 

 to Keitli, a vegetable is an organised and living substance springing from a seed or gem, 

 which it again produces ; and effecting the developeraent of its parts by means of the 

 intro-susception and assimilation of unorganised substances which it derives from the 

 atmosphere or the soil in which it grows. The definition of the animal is the counter- 

 part : an animal is an organised and living being proceeding from an egg or embryo, 

 which it again produces, and effecting the developement of its parts by means of the 

 intro-susception of organised substances or their products. For all practical purposes, 

 perhaps plants may be distinguished from animals with suflficient accuracy by means of 

 the trial of burning ; as animal substances in a state of ignition exhale a strong and 

 phosphoric odour, which vegetable substances do not. 



Chap. V. 

 Vegetable Pathology, or the Diseases and Casualties of Vegetable Life. 



1671. As plants are, like animals, organised and living beings, they are, like animals, 

 also liable to such accidental injuries and disorders as may affect the health and vigour, 

 or occasion the death, of the individual. These are wounds, accidents, diseases, and 

 natural decay. 



Sect. I. Wounds and Accidents. 



1672. A wound is a forcible separation of the solid parts of the plant effected by means 

 of some external cause, intentional or accidental. 



1673. Incisions are sometimes necessary to the health of the tree, in the same manner, perhaps, as 

 bleeding is necessary to the health of the animal. The trunks of the plum and cherry tree seldom expand 

 freely till a longitudinal incision has been made in the bark ; and hence this operation is often practised 

 by gardeners. If the incision affects the epidermis only, it heals up without leaving any scar ; if it pene- 

 trates into the interior of the bark, it heals up only by means of leaving a scar ; if it penetrates into the 

 wood, the wound in the wood itself never heals up completely, but new wood and bark are formed above 

 it as before. . . 



1674. Boring is an operation by which trees are often wounded for the purpose of making them part 

 with their sap in the season of their bleeding, particularly the birch tree and American maple. A 

 horizontal, or rather slanting, hole is bored in them with a wimble, so as penetrate an inch or two into 

 the wood ; from this the sap flows copiously ; and though a number of holes are often bored in the same 

 trunk, the health of the tree is not very materially affected. For trees will continue to thrive, though 



