1^ 



4 



^cfidcs tlic capillary tubes>, &ct. before-mentioned, 

 kWe are other larger veflels, which fome call venal 

 veflels, which are dilbofedbh tlie outfide of the arte- 

 rial veflels, between the wood and the inner bark, and 

 lead down t6 the covering df the inward root. Thefe 

 veflels are fuppofed to contain the liquid fap found in 



plants in the Ipring, &Ci 



The Rev. Dr. Hales tells us in his excellent treatife 

 oji Vegetable Statics, thit, in order' to find whether 

 there was any lateral communication of the fap and 

 fap- veflels, as there is of the blood in animals, by 

 means of the ramifications and lateral communica- 

 tions of their veflels \ he took a young oak-branch, 

 fe^eri or^ight inched diameter, at its tranfverfe cut, fix 

 feet high, and full of leavfes ; and having cut a large 

 gap to the pith, feven inches from the bottom, and 

 of an equal depth the whole length, and alfo cut an- 

 other gap four inches above thit on the oppofite fide, 

 he fet the end of the fl:em in water, and in two nights 

 and two days time it imbibed and perfpired thirteen 

 ounces; while another like oak-branch, fomewhat 

 bigger than that, but with no notches cut in its fl:em, 

 imbibed twenty-five ounces. ' 



Froni this and many other experiments he there men- 

 tions, he fays, we fee a moft free lateral communi- 

 cation of the fap and fap-veffels,' thofe great quanti- 

 ties of liquor having pafled laterally by the gaps ; in 

 that, by feveral experiments on cylinders of wood, 

 little evaporated by the gaps. 

 The bark is the exterior part of trees, ferving them 

 for a Mn or Covering : it is gcneralljr of a fpongy tex- 

 ture, and communicates with the pith by a multipli- 

 city of fmall fibres pairing through the capillary tubes, 

 of which the wood confifl:s : fo that the roots having 

 imbibed the proper' nutriment of the tree, it is carried 

 Up by the warmth of the fun, through the fine arte- 

 rial veflel of the tree, to the top of it ; and being 

 there condenfed by the cold, it does, by its own gra- 

 vity, return down bytheveflTels which lie between 



the wood and the innefr bark, which perforni the of- 

 fice of veins -, and as it pafles by, leaves fuch parts 

 of its juice as the texture of the bark will receive, 

 and requires for its fupport. 



Some are of opinion, that" that foft whitifli rind, or 

 fubftance, whicii lies between the inner bark arid the 

 wood, does the office of veins : and fome call this a 

 third bark, arid fuppofe it to differ from the other in 

 .riothing but having clofer fibres, and that it contains 

 the liquid fap, gums, &c. which are found in the 

 plants in the fpring and fummer months, which har- 

 dens by degrees, by means of the fap it tranfmits, and 

 is imperceptibly conveyed into the woody part of the 

 tree. - - • - • 



The bark ferves for divers purpofes ; for it not only 

 tranfmits the nutritious juices of the plants, but alfo 

 contains divers fat oily humours, to defend the inner 

 parts from the injuries of the weather. As animals 

 ^re furnilhed with a panniculus adipofus, ufually re^ 

 plete with fat, which invefl:s and covers all the ficfliy 

 parts, and fcreens them from external cold j fo are 

 plants encompafled with a bark, replete with fat juices, 

 by means whereof the cold is kept out, and, in win- 

 ter-time, the fpicul^ of ice prevented from fixing 

 and freezing the juices in their veflels -, whence it is, 

 that fome forts of trees remain ever-green throughout 

 the year, by reafon their barks are more compaft, 

 and contain a larger quantity of oil than can be fptnt 



and exhaled by the fun. 



The pith is the inward central part of a tree or plant, 

 anfwering to the medulla, or marrow of an animal. 

 As for its fubftance, it confifts of little tranfparent 

 globules, chained or linked together, fomewhat like 

 the bubbles that compofe the froth of liquor. 

 Some fuppofe, that the circulation of the fap is ef- 

 fefted by means of the pith, others by the bark, and 

 others by the wood. '* 



Bdrelli, in his book De Motu Animalium, fuppofes 

 the tender growing flioot to be diftended like foft wax, 

 by the expanfion of the tnoifl:ure in the Ipongy pith ; 

 which dilating: moilhire, he concludes, is hindered 



f ' 



r - « 



from returning back, while it expands by the Ipongi^ 

 nefs of the pith without the help of valves. ; 

 And the Rev. Dr. Hales is of opinion, that it is very 

 probable, that the particles of water that imrhediately 

 adhert tb, and are ftrongly iinbibed into, and attradt* 

 ed by, every fibre of the fpongy pith, will fuffer fome 

 degree of expanfion before they can fee detached bV" 

 the warmth of the fun from each attracting fibre ; and, 

 confequently, the mafs of fpongy fibres, of which the 

 pith confifl:s, mufl: therefore be extended. 

 And that the pith may be the more ferviceable (ot 

 this purpofe, nature has provided in moftlhoots i 

 fl:rong partition at every knot, which pdrtitiofis ferv^ 

 not only as plinths or abutments for the dilating pith? 

 to exert its force on, but alfo to prevent the too free 

 retreat of the rarefied fap from the pith. 

 But a dilating fpongy fubft:ance, by equally expand- 

 ing itfelf every way, would not produce an oblong 

 flioot, but rather a gjobous one, like an apple 5 to 

 prevent which inconvenknce it is obfervable, that 

 nature has provided feveral diaphragms, befides thofe 

 at each knot, which are placed at fmall diftarices acrdfs 

 the pith, thereby preventing its too great htttil dxh^ 

 tation. ' 



Thefe are very plain to be feen in the fhoors of the 

 Walnut-tree, and the fame may be obferved in the 

 pith of the branches of the Sun-flower, and feveM 

 other plants, where thofe diaphragms are not to be 

 diftinguiflied while the pith is friU and replete with 

 moifture ; yet when it dries IKp, they are often plain 

 to be feen. And it is farther to be obferved, that 

 where the pith confifts of diftinft veficles, the fibres 

 of thofe veficles are often found to run horizontally, 

 whereby they can the better refift the too great lateral 

 relaxation of the root. 



The trunk and branches of a tree, bear a refemblance 

 to the exterior menfibers kxid limbs of an animal, 

 which it may fubfift without,- though th^ rotting arid 

 mortification of them oftentimes occafion a total de- 

 ftruftion of it. Accordingly the like effefts ar^fotJnd 

 from the wounding or lopping of a tree, as froiii the 



wounding or cutting off* a limb, an extravafation, cal- 

 lus, or the like. 



A leaf is 'part of a plant extended into length and 

 breadth in fuch a manner, as to have one fide diftin- 

 guifliable from the other, l^he leaves, according ta 

 Malpighius, confift of fo many interwoven utricles, 

 as to be not much unlike a pulmonary net, andfervl* 

 inftead of lungs to the plant. As the perfpiration 

 and refpiration are chiefly performed thereby, thofe 

 veflels are very confpicuous when the leaves are dif- 

 fered. In the day-time, when the heat hath rarefied 

 the mounting juices, fo as to ' become Ipecifically 

 lighter than the air, they flow out through the pores 

 of the leaves, and evaporate, which is the occafion of 

 the leaves becoming fo flaccid ih very hot weather ; 

 bur in the night, when by the cold the juices are 

 more condenfed, then the leaves are eredted again, and 

 draw in a great ftiare of nourilliment from the air. 

 Thefe leaves we may obferve to be of different tex- 

 tures on each fide, the upper furface being for the 

 moft part fmooth, the better to ftioot off* the redun- 

 dant moiflAire, while the under furface is many times 

 of a rough and cottony texture, by which it is capa- 

 ble of retaining the moifture ; for which reafon we 

 find, if by bad management, &c. the flioots of trees 

 are nailed to a wall, &c. fo as to turn the furfaces of 

 the leaves the wrong fide upwards, the ftioots will be 

 at a ftand, until the leaves have obtained their proper 

 diipofition. Thefe leaves, as the learned Dr. Hales 

 oblerves, are carefully diftributed at fmall diftances 

 throughout the whole length of the fliobts, andferve 

 as fo many jointly-afting powers, placed at different 

 ftations, thereby with more eafe to draw plenty of fap 

 to the extending root. " ^ ■ 



A fioWer is the more terider part of a plant, remark* 

 able for its colour, or form, or both, cohering with 

 the rudiment of the frviit^ and contains the organs of 

 generation > fome of thefe flowers contain the male 

 organs, as the ftamiqa aiid ^pice^j, wtuch a^e loaded 



7 yith 



