636 



FARMERS' REGISTER. 



[No. 11 



pands by ihe assimilalion of a variety of new ali- 

 ments, and by powers entirely different from those 

 of common inorganic matter; but there seems to 

 be no system of nerves, as in animals, which is 

 essential to irritability. We know so little of the 

 refined powers and properties of matter, that we 

 can give little more than vague hypotheses as to 

 the cause of the movement ol" the fluids in the ve- 

 getable cells or tubes; yet it is impossible not to 

 allow common material agents a much greater 

 share in producing this phenomenon, than they 

 exercise in animal life. 



Whoever will peruse any considerable part of 

 the Vegetable Statics of Hales, must receive a 

 deep impression of the dependence of the motion 

 of the sap upon physical causes. In the same 

 tree, this sagacious person observed that in a cold 

 cioudy morning, when no sap ascended, a sudden 

 change was produced by a gleam of sunshine of 

 half an hour, and a vigorous motion of the fluid. 

 The alteration of the wind from south to the north 

 immediately checked the effect. On the coming 

 on of a cold afternoon after a hot day, the sap 

 that had been rising began to fall. A warm 

 ehower and a sleet storm produced opposite el- 

 Jecfs. 



Many of his observations likewise show that 

 the different powers which act on the adult tree, 

 produce different effects at different seasons. 



Thus, in the early spring, before the buds ex- 

 pand, the variations of the temperature, and 

 changes of tlie state of the atmosphere with re- 

 gard to moisture and dryness, exert their great ef- 

 fects upon the expansions and contractions of the 

 vessels; and then the tree is in what is called by 

 gardeners its bieedisg season. 



"When the leaves are fully expanded, the great 

 determination of the sap is to these new organs. 

 And hence a tree which emits sap copiously i'rom 

 a wound whilst the buds are opening, will no 

 longer emit it in summer when the leaves are per- 

 tect; but in the variable weather, towards the end 

 of autumn, when the leaves are ialling, it will 

 again possess the power of bleeding in a very 

 slight degree in the warmest days: but at no other 

 times. 



In all these circumstances there is nothing truly 

 analogous to the irritable action of animal sys- 

 tems. 



In animal systems the heart and arteries are in 

 constant pulsation. Their functions are unceas- 

 ingly perlbrmed in all climates, and in all seasons; 

 in winter, as well as in spring; upon the arctic 

 snows, and under the tropical suns. They neither 

 cease in the periodical nocturnal sleep, common to 

 most animals; nor in the long sleep of winter, pe- 

 culiar to a few species. The power is connected 

 with animation, is limited to beings possessing the 

 means of voluntary locomotion; it co-exists with 

 the first appearance of vitality; it disappears only 

 with the last spark of life. 



As the operation of the diflTerent physical agents 

 upon the sap vessels o) plants ceases, and the fluid 

 becomes quiescent, the materials dissolved in it by 

 heat are deposited in the cells of the alburnum ; 

 and in consequence of this deposition, a nutritive 

 matter is provided for the first wants of the plant 

 ' in early spring, to assist the opening of the buds, 

 and their expansion, when the motion from the 

 want of leaves .is as yet feeble. 

 This beautifial principle in the vegetable econo- 



my was first pointed out by Dr. Darwin ; and 

 Mr. Knight has given a number of experimental 

 elucidations of it. 



Mr. Knight made numerous incisions into the 

 alburnum of the sycamore and the birch at differ- 

 ent heights ; and in examining the sap that flowed 

 from them, he ibund it more sweet and mucilagi- 

 nous in proportion as the aperture from which it 

 flowed was elevated ; which he could ascribe to 

 no other cause than to its having dissolved sugar 

 and mucilage, which had been stored up through 

 the winter. 



He examined the alburnum in diflTerent poles of 

 oak in the same Ibrest ; of which some had been 

 felled in winter, and others in summer ; and he 

 always found most soluble matter in the wood 

 felled in winter, and its specific gravity was like- 

 wise greater. 



In all perennial trees this circumstance takes 

 place; and likewise in grasses and shrubs. The 

 joints of the perennial grasses contain more sac- 

 charine and mucilaginous matter in winter than 

 at any other season ; and this is the reason why 

 the florin or agrostis alba, which abounds in 

 these joints, affords so useful a winter food. 



The roots of shrubs contain the largest quantity 

 of nourishing matter in the depth of winter ; and 

 the bulb in all plants possessing it is the recepta- 

 cle in which nourishment is hoarded up during 

 winter. 



In annual plants the sap seems to be fully ex- 

 hausted of all its nutritive matter by the produc- 

 tion of flowers and seeds ; but if parts of annual 

 plants, having leaves and buds, be detached and 

 kept, so that thej^ do not expend themselves by 

 affording blossoms or seeds, the same individual 

 life may be preserved through many years. It 

 appears, therefore, as Mr. Knight observes, to be 

 habit only, not life, that is annual in such plants. 



When perennial grasses are cropped very close 

 by feeding cattle late in autumn, it has been often 

 observed by farmers that they never rise vigorously 

 in the spring; and this is owing to the removal of 

 that part of the stalk which would have afforded 

 them concrete sap, their first nourishment. 



Ship-builders prefer for their purposes that kind 

 of oak timber afforded by trees that have had their 

 bark stripped oflT in spring, and which have been 

 cut in the autumn or winter ibilowing. The reason 

 of the superiority of this timber is, that the con- 

 crete sap is expended in the spring in the sprouting 

 of the leaf; and the circulation being destroyed, 

 it is not Ibrmed anew ; and the wood having its 

 pores free from saccharine matter, is less liable to 

 undergo fermentation from the action of moisture 

 and air. 



In perennial trees a new alburnum, and conse- 

 quently a new system of vessels is annually pro- 

 duced, and the nutriment for the next year deposit- 

 ed in them ; so that the new buds, like the plume 

 of the seed, are supplied with a reservoir of mat- 

 ter essential to their first developement. 



The old alburnum gradually loses its vascular 

 structure, and, being constantly pressed upon by 

 the expansive force of the new fibres, becomes 

 harder, denser, and at length becomes heart-wood; 

 and in a certain time obeys the common laws of" 

 dead matter, decays, decomposes, and it is convert- 

 ed into aeriform and carbonic elements; into those 

 principles from which it was originally formed. 



The decay of the heart-wood seems to consti- 



