293 



PHY 



THE UNIVERSAL HERBAL; 



PHY 



covered with ice, without suffering the least injury. In the 

 noithern hemisphere of our globe there are many and exten- 

 sive tracts of Pine-trees, which resist with their evergreen 

 branches the most severe winter cold. From these observa- 

 tions it follows, that each .plant, according to its species, 

 possesses a peculiar degree of warmth, which defends it 

 against the inclemency of the weather. But this heat in ve- 

 getables is not of such a nature as to enable us to judge of 

 its peculiar degree by our senses. We know that every ani- 

 mal has a certain degree of heat. We find a frog or lizard 

 cold, although nature has, given them a certain degree of heat. 

 The temperature of plants is such as to enable them to resist 

 both heat and cold. If, in a hot summer day, we touch some 

 ground which is much exposed to the rays of the sun, and 

 immediately after put our hand on green grass, equally ex- 

 posed to them, we shall find the ground much hotter than 

 the grass. Fruits, though much in the sun, will be cool, ] 

 whereas a glass full of water will be quite warm in a much 

 shorter time. Sonnerai discovered in the island of Lucon a 

 rivulet, the water of which was so hot, that a thermometer 

 immersed in it rose to 174 Fahrenheit. Swallows when fly- 

 ing seven feet high over it, dropped down motionless. Not- 

 withstanding this heat, he observed on its banks two species j 

 of Aspalathus and the Vitex Agnus Castus, which with their 

 roots swept the water. In the island of Tanna, Messrs. For- i 

 sters found the ground near a volcano as hot as 210 Fah- | 

 renheit, and at the same time covered with flowers. Hence 

 it naturally follows, that plants, like animals, have a peculiar 

 temperature, according to their native countries, which they 

 cannot exceed without injury. The experiments of Mr. J. 

 Hunter and Schoepf shew us the same thing. The first put 

 a Scotch fir, three years old, in a freezing mixture of between 

 15 and 17 Fahrenheit. The youngest shoot froze; the fir 

 was again planted, the young shoot remained flaccid, but the 

 first and second were fresh. Of young plants of oats, which 

 had only three leaves, one leaf was exposed to artificial cold 

 at 22, and was instantly frozen. The root was put into the 

 same cold mixture, but remained uninjured. He then planted 

 it, and all its parts grew, except the leaf, which had been 

 frozen. The same experiment he repeated in a young bean ; 

 a leaf of it was frozen in an artificial freezing mixture, and 

 another fresh leaf was bent in the middle upon itself, put 

 into a leaden vessel, and along with it the frozen leaf, which 

 had been previously thawed. He afterwards put the vessel 

 into a freezing mixture. The surface of the fresh leaf froze 

 as far as it came in contact with the vessel between 15 and 

 17, the atmosphere being at 22. The frozen leaf froze 

 much sooner. These experiments were repeated, and at- 

 tended with the same result. The juice of spinnage and cab- 

 bage, when squeezed out, conjealed at 29, and thawed 

 again between 29 and 30. This juice was frozen in a leaden 

 vessel, and then put into another, with a cold mixture at 28. 

 The leaves of a growing fir-shoot, and a bean-leaf, were put 

 upon the frozen liquid, which in that place thawed in a very 

 few minutes. The leaves had the same effect when removed 

 to other frozen spots. 



" The anatomical investigation of vegetables explains the 

 nature of their internal parts. The following organs have 

 been discovered in them; air vessels, adducent vessels, redu- 

 cent vessels, lymphatic vessels, cellular texture, vegetable 

 fibre, and glands. These parts are visible only through mag- 

 nifying glasses, either by subjecting them to maceration, or 

 by putting them in newly cut pieces under a microscope. 

 Some of them, particularly the adducent vessels, may be 

 filled with a strong coloured liquid, by which means they are 

 so much the more easily observed. This, however, is the 



case only with a few. The injection of vessels with a coloured 

 liquid is accomplished by putting the stalk of a plant into a 

 decoction of brasil wood, and placing it in a warm tempera- 

 ture. Injections of this kind do not succeed with all plants, 

 but are particularly suitable to the Impatiens Balsamina. 

 The air vessels, are thin, hollow, corrugated vessels, smooth 

 within, and running perpendicularly through the plants. 

 They are conductors of air, and never change their diameter, 

 but uniformly remain open even in the hardest wood. How 

 they are connected with the pores of the epidermis, has not 

 yet been discovered by any observations. The adducent 

 vessels, are situated close to the air vessels, and have a double 

 direction. They either proceed in a straight line with the 

 air vessels, or they twine around them in wide or narrow in- 

 terstices, but they are often involved in spiral windings, so 

 close that no interstice can be perceived. When they have 

 this twisted appearance, they are called spiral vessels. In 

 plants we discover twisted vessels of greater or less extent, 

 as well as those which run straight out in lines. There are 

 also vegetables in which they are never twisted, but uniformly 

 proceed in straight lines ; for example, Sagittaria sagittifolia, 

 and all the Filices. It is a singular circumstance, that in the 

 Filices, bundles of these last mentioned vessels are surround- 

 ed with a peculiar sort of membrane which is quite abstracted 

 from the cellular texture, a section of which shows it to be 

 more or less circular, lunated, or of a different form. 1'hese 

 vessels are much more delicate than air vessels in their dia- 

 meter, and even do not retain the same figure. They visibly 

 grow larger, become rough, and when beginning to harden 

 have their interior covered with contiguous fibres; in the 

 end they are almost completely obstructed. Reducent vessels, 

 descend between the cellular texture, and are variously accu- 

 mulated. Sometimes they take a horizontal direction. Hed- 

 wig supposes them to be intended for the purpose of trans- 

 piration. They are more delicate than the adducent vessels. 

 Lymphatic vessels, are found upon the epidermis. They are 

 extremely delicate, run singly, and are reticularly united. 

 The circle or quadrate which is described on these vessels, 

 has usually in its centre'an aperture, which, however, has no 

 connexion with the vessels. The reticular form varies greatly 

 in vegetables. It is constantly found in every species, and 

 in a few is subject to some alterations. Thus, for example, 

 in the Lilium Chalcedonicum, these vessels run in an undulat- 

 ing manner, and describe very irregular oblong figures or 

 even rhombi ; in the Allium Cepa they do not undulate, but 

 proceed in an oblique direction parallel to one another by 

 short continuations of the sides ; in the Dianthus Caryophyl- 

 lus they describe parallelograms which terminate pretty regu- 

 larly. This reticular texture covers all the parts of plants, 

 only the apertures which it surrounds are not always obvious. 

 On the root, on the surface of the leaves, on the interior side 

 of the valves of the calix, especially when they are coloured, 

 on the interior of the petals, on the nectaria, in stamina and 

 pistils, no pores can be discovered, and only the cicatrice has 

 them sometimes. That this kind of net on the cortex of vege- 

 tables is not occasioned by the pressure of the cellular tex- 

 ture, but consists of real vessels, appears to be beyond all 

 doubt. The cellular texture, is a very delicate membrane, di- 

 vided into an infinite number of variously formed small 

 spaces, which are closely connected with one another. It sur- 

 rounds the vessels, and occupies the internal as well as the ex- 

 ternal interstices, covers both surfaces of leaves, and is most 

 plentiful in the juicy plants and fruits. The pith of vegetables 

 is a more dense cellular texture, distinguished by its bright 

 white colour, by its. finer and more compressed cells, and by 

 its spungy appearance. The juices conveyed in the cellular 



