306 



PHY 



THE UNIVERSAL HERBAL: 



PHY 



promotes vegetation. The branch of a Service tree was put 

 into pure water, another into a solution of muriate of ammo- 

 nia; in 24 hours the former imbibed 5-12ths, the latter 

 10-12thsof the liquid; and hence we may draw the probable 

 conclusion, that the muriate of ammonia, by its stimulus, 

 increased the activity of the vessels. Nitrate of potash is 

 used by the Dutch gardeners as a means of promoting growth. 

 The bulbs of Narcissuses, Hyacinths, and other vegetables, 

 grow much faster in water where this neutral salt is dissolved. 

 Tromsdorf found also that a sprig of the Mentha piperita 

 became 378 grains heavier in a solution of nitre, whereas a 

 sprig in common water gained but 145 grains in weight. 

 Barton, however, directly maintains the contrary, because a 

 few grains of nitrate of potash killed a Kalmia. But it is 

 easy to conceive that a moderate stimulus to some plants, 

 may be over violent and destructive toothers. Barton found 

 that in water in which camphor was diffused, a decayed twig 

 rapidly recovered, which did not happen when it was placed 

 in common water. A decayed branch of Liriodendron tuli- 

 pifera, and a withered flower of the yellow Iris, recovered 

 in it, and remained long fresh. I myself tried this with a 

 branch of Silene pendula, the flowers of which were quite 

 shrivelled ; in an hour's time I found the petals again per- 

 fectly expanded, as if just evolved. Is it the hydrogen of 

 the camphor which stimulates the vegetable fibre to such a 

 degree, as to produce this phenomenon? or is it a conse- 

 quence of the composition of the camphor, that only the 

 exact proportion of carbon, which is found combined with 

 hydrogen in camphor, can stimulate the fibres ? This remains 

 to be determined. Light likewise is a very powerful stimulus 

 of the vegetable fibre. Every body knows that hot-house 

 plants incline their stalks and leaves always towards the 

 windows. A plant which has been confined for days in a 

 dark room, will, as soon as some light is admitted, however 

 small the aperture be through which it passes, bend its stalks 

 towards the light. Who does not know, that the species of 

 Lupinus, especially Lupinus luteus, turn in the open air 

 their leaves and stalks towards the sun, and follow its course 

 in so steady a manner, as to enable us to specify the hour of 

 the day from their direction ? Light is farther of particular 

 service to vegetables in promoting the decomposition of the 

 absorbed water, and separation of the oxygen ; for when this 

 oxygen gas is accumulated in vegetables, all their parts 

 become white, as may be seen from plants which vegetate 

 in the dark. Even the light of a lamp effects the separation 

 of the oxygen, as an experiment, of which I was eye-witness, 

 fully proves, viz. that of Humboldt, who rendered Lepidium 

 sativum, which had grown up in a dark cellar, green, by the 

 faint glimmering of a lamp kept under it several days. All 

 plants cannot support the stimulus of strong and constant 

 light. There appears to be a determinate degree of this sti- 

 mulus, which they cannot without injury exceed. As young 

 plants are much more susceptible than grown up ones, they 

 thrive best in the shade. All forest plants are destroyed by 

 too much light. This is proved by the observations of Medi- 

 cus, Desfontaines, and Uslar, who found that the irritabi- 

 lity of plants is strongest in the morning, fainter at mid-day, 

 and fainter still in the evening. Sennebie'r has made the 

 experiment of separating the rays of light, in order to dis- 

 cover which of them is most favourable to vegetation ; and 

 he found, that plants of Lettuce grow best in the yellow, 

 and next in the violet. Those on which the invisible ray 

 fell, came nearest to those which stand free in the collected 

 light. The irritability of the vegetable fibre is destroyed by 

 all stimuli when they are too powerful or too long continued. 

 Every stimulus must be proportioned to the irritability of 



the fibre ; in proof of which may be adduced all subterrane- 

 ous plants and all the species of Boletus : for the knowledge 

 of which we are indebted to the researches of Scopoli and 

 Humboldt. These plants require a very small quantity of 

 oxygen to promote their growth, and therefore as soon as 

 they are brought into the open air, they decay. This is 

 even proved by the well-known observation, that rooms or 

 repositories which are fusty or mouldy, are freed from this 

 inconvenience by the admission of air. Opium will destroy 

 the irritability of plants ; by it the irritability of Hedysarum 

 gyrans and Mimosa pudica was greatly impaired, and almost 

 completely destroyed. Vegetables die very soon in carbonic 

 acid gas ; as well as in nitrogen and hydrogen gas. In the 

 last of these, plants die immediately ; but if it be mixed with 

 a little oxygen gas, they live for a short while, and grow very 

 luxuriantly. Mr. Humboldt, on the 14th February, 1792, 

 put a germinating bulb of the Crocus vernus, which he had 

 planted, into one of the celebrated mines of Freyberg, several 

 fathoms under ground. In this mine, the air was so much 

 contaminated with hydrogen gas, that his candle was extin- 

 guished, and his lungs became sensibly affected. The germ 

 of the bulb soon evolved, the leaves became green, the 

 flowers yellow, and the anthers even full of pollen ; but on 

 the 17th the whole plant suddenly began to putrefy. Several 

 plants shewed the same result. The hydrogen gas cannot 

 however be considered as a stimulus of vegetables, as in its 

 pure state it kills plants, and only when mixed with oxygen 

 shews the above phenomena. Plants live so long only, as 

 they can exhale oxygen ; when this stops, they are gone. In 

 the same manner, Sennebier and Ingenhouss observed that 

 plants confined in hydrogen gas, emitted oxygen day and 

 night ; but that when the oxygen gas was consumed, they 

 could no longer subsist. 



"The above numerous observations are sufficient to prove 

 that vegetable sap is not put in motion by mechanical prin- 

 ciples, but that it is carried forward by the irritability pecu- 

 liar to plants. The ascent of sap in warm weather, and the 

 descent of it in cold weather, can no longer be argued ; but 

 experiments, and the analogy between plants and animals, 

 clearly point out a circulation. For how could the juices 

 of trees, which during winter continue bare, without foliage, 

 and without discovering any symptom of vegetation, be at 

 all preserved, if in the long succession of cold weather the 

 moisture which is found in the vessels were constantly to 

 descend. We should at last necesarily find the branches 

 quite destitute of fluid, which is never the case. Nor is the 

 cessation of sap, or the congelation of it in very cold wea- 

 ther, more admissible. We know from experience, that when 

 the juices of delicate exotic plants are coagulated by cold, 

 they must die. The circulation of sap must therefore take 

 place in them, as they cannot, on account of the unfavour- 

 able season, make new shoots still, and survive; and, though 

 much less vigorous, they appear to exist in the same manner 

 as hybernating animals, such as the marmot and dormouse, 

 which, during the winter, like amphibious animals and some 

 insects, fall into a profound sleep, and are awakened first 

 with the returning warmth of spring. Experiments have not 

 yet discovered how the circulation of blood in these species 

 of animals adapts itself to the season of the year. What has 

 been adduced as proof of the ascent and descent of the sap 

 in plants, is the important, but altogether mistaken pheno- 

 menon, that after the middle of January, with us after the 

 20th, the sap enters trees. At this period it is thought to 

 descend, to be ready in the spring. But whoever thinks 

 that trees, shrubs, or herbs, are dead in winter, or without 

 action, is much mistaken. During the whole summer, th 



