PHY 



OR, BOTANICAL DICTIONARY. 



PHY 



306 



toria, growing in Ceylon, has on the apex of its leaves a 

 leaf-like ascidium, which at times opens and closes, and is 

 even filled with water. This takes place also in a species of 

 this genus indigenous in Amboyna. Of all plants, however, 

 in this respect the most singular is the Hedysarum gyrans, 

 growing on the banks of the Ganges. It has trifoliate leaves, 

 of which the central one is larger than the two others. All 

 these leaves move spontaneously. The large one rises back- 

 wards, up and down, the two smaller leaves at the sides have 

 the same movement, only somewhat vigorous. Laying hold of 

 these leaves, and then removing the hand, quickens their 

 motions, as if they were to make up for the lost time, till at 

 last they return to their former slower motion. No particular 

 stimulus seems to act on them, and they do not contract like 

 other irritable plants. Nor does this motion of the leaves de- 

 pend on sun-light, for they move in light as well as in the dark, 

 even when the plant is perfectly asleep. It is besides remark- 

 able, that the leaves in the height of erection, and during 

 very warm days, like the animal muscular fibre, have a tre- 

 mulous motion. The stipules and braeteee agree perfectly 

 with the leaves with respect to anatomical structure. The 

 floral leaves are sometimes coloured. 



"From what has been said respecting the internal nature 

 and chemical constituents of vegetables, and from the gene- 

 ral observations which have been made, we are enabled, as 

 far as these remarks extend, to form some conclusion respect- 

 ing the vital process in plants. Like animals, they are pro- 

 vided with vessels, which contain juice ; they are susceptible 

 to the application of stimuli, and thus are irritable ; they also 

 correspond with animals in their evolution and formation. 

 Hence we might infer that they must have a circulation of 

 sap. In our days, hardly any one will support Jampert, in 

 his attempt to prove, on mathematical principles, that plants 

 have no vessels, as their existence has been fully ascertained 

 by Grew, Malpighi, Mustel, Molclenhawer, Hedwig, &c. 

 &c. and as every one who doubts may be convinced of this 

 ' truth by ocular demonstration. Physiologists, however, do 

 not agree in every respect. Hales considered the motion of 

 sap in vegetables as the ascent of a fluid in a capillary tube, 

 and alleged that it was carried forward merely by attraction, 

 such as by light and heat. Malpighi was" the first who 

 ascribed irritability to the vessels, and asserted that their 

 diameter was contracted and enlarged. He even affirms, 

 that he observed, in the spiral vessels, a peristaltic motion, 

 similar to that of the animal intestines. But he must have 

 been deceived here, as the spiral vessels dry immediately 

 when exposed to the air, and roll together in consequence of 

 their extraordinary fineness. Corti admits the irritability of 

 the vessels. Under the microscope, he pretends to have 

 observed in the vessels of sixty-five plants a motion of the 

 juice from joint to joint; and he supposes that every knot 

 in unison with its interstice has a peculiar circulatory system 

 quite independent of the other parts. Miller adopted the 

 opinion of Hales, that there was merely a rise and fall of the 

 sap, without a-ny fixed circular motion; that heat occasioned 

 the rise, and cold the fall, of the sap. Walker, who attempted 

 to investigate the motion of the sap in trees which bleed in 

 spring, affirms, that in spring the sap first begins gradually 

 to ascend in the root, and at last rises to the top, and that 

 this depends on the temperature of the external air, but that 

 the juices never descend. Owing to this, the buds at the 

 extremity are developed first. The sap is supposed to ascend 

 between the bark and the wood ; but this effect is produced 

 not by heat alone, but by its co-operation with an internal 

 unknown cause. He does not absolutely reject the opinion 

 of there being a circulation, but only supposes 'that the tree 



before its evolution has quite a different motion of sap from 

 what it has when in leaf. Various conjectures have been 

 formed by other physiologists respecting the circulation of 

 sap in the vegetable kingdom. Some think that the sap 

 ascends only through the vessels of the inner bark. Others 

 assert that it ascends to the wood through the ' roots, and 

 descends through the cortex. Of this opinion are those who 

 have injected plants with coloured liquids. From their obser- 

 vations it would appear that the coloured juice proceeds from 

 the substance of the root into the wood, and hence is com- 

 municated to the leaves, from which it finds its way back 

 through the cortex. Brugmann has endeavoured to prove 

 the irritability of vessels, by shewing that the amputated 

 branches of the Euphorbia lathyris and myrsiitites, which 

 emit a great quantity of milk, cease to do so as soon as the 

 cut part is anointed with a solution of alum and sulphate of 

 iron, so diluted that it leaves no stain on paper. Van Marum 

 repeated this experiment, but did not obtain the same result. 

 Uslar, however, has observed that the amputated stalk of 

 Euphorbia exigua and sylvatica, when immersed in a solution 

 of alum or acetous acid, immediately, or at least in a short 

 time after, ceased to flow. Van Marum demonstrates, by 

 several remarkable experiments, the irritability of vessel*. 

 He poured an electric stream over the branches of Euphorbia 

 lathyris, as well as through the whole plant of Euphorbia 

 esula and cyparissus, for the space of 20 to 30 seconds. On 

 intersecting them, it was found that they did not emit any 

 milky juice, though, by compression, some of it was observed 

 to drop. He made the same experiment on the boughs of 

 the Ficus carica, which were exposed for 15 seconds to an 

 electric stream. Girtanner asserts, that oxygen is a stumulus 

 to plants; that oxygen has a closer connection with the vege- 

 table fibre than with other bodies ; that all bodies which 

 rapidly absorb oxygen, are stimuli to plants, and must pro- 

 mote their growth. According to this theory, the experi- 

 ments of Mr. Humboldt, which he made on the germination 

 of plants, may be very well explained; and the observations 

 of Ingenhouss and others, confirm the opinion that corn and 

 other vegetables, in a bad soil, when sprinkled with well- 

 diluted sulphuric acid, grow just as well as if they had been 

 plentifully manured. We learn also from chemistry, that 

 oxygen from the atmosphere very easily combines with the 

 different species of earths and stone, particularly with vege- 

 table mould. It is well known to every gardener and forester, 

 that trees planted in spring grow so much better by having had 

 their holes digged in autumn, which during the winter were 

 exposed to the influence of the air. Experiments have aJso 

 shewn, that soils which have been dug into loose heaps of 

 earth frequently stirred, and then exposed for half a year to 

 the influence of the air, produce a richer crop than if they 

 had been manured, and retain this fruitfulness longer than 

 by the application of manures. But, besides the mere oxygen, 

 there are other bodies which act as stimuli upon plants. 

 Most of these, however, appear only in an active state, for 

 this reason, that they either contain oxygen or dissolve it. 

 Well or river water, considered as an aliment, being decom- 

 posed in the vegetable process, sometimes also constitutes a 

 stimulus. Rain water is much more beneficial to plants than 

 any other, because, according to Hassenfraz's investigation!, 

 it contains more oxygen. Caloric is an excellent stimulus to 

 vegetables, as it renders oxygen gaseous, and moistures more 

 fluid : consequently the influence of this matter becomes 

 more powerful; only, the degree of it must be proportioned 

 to the vegetable fibre. Thus, plants at the tropics will sus- 

 tain more heat than mountain plants, or those at th poles. 

 Muriate of ammonia, according to Brugmaun's observations, 



