155 



Proceedings of Learned Societies. [Sept. 1, 



by 'siny general cxtcnnon of paitsalicady 

 Ibniit'fl : and the new niattfr whicli is 

 thus luccefllvely arlderl dcfccnds in a liuid 

 ftatc from tlic cotyledons. On this fluid, 

 and on the vcirttablc tibrcs and vtilels 

 whiHl foft and flc\it)lc, and whilft the 

 mattei- whieh conijjofcs them is chang- 

 ing from a fluid to a tofid ftate, gravita- 

 tion would ojicrate Intliciently to give an 

 inclination downwards to the point of the 

 rachcie. 



As the radicle is incroatcd in length 

 only by parts fucccffivtly added to its 

 point, the gernicn, on the contrary, 

 elongates by a general cxtcnfion of its 

 parts previiinlly organized ; and its \c{- 

 JJL'ls and iibres appear t(j extend theni- 

 fclves in proportion to the ipiantity of 

 nutriment they receive. " If the motion, 

 (lays I\]r. Knight), and confcriuent dit- 

 tribulion of the tnic fiiji, be inllni'uced 

 by gravitation, it follows, that when tiie 

 g«:rmen at its fird emiiiion, or fubi'e- 

 cjiicntly, deviates from a perpendicular 

 direction, the faj» rnntV accumulate on 

 it> under lide : and I iiave found, in a 

 great variety of evperiments on tlie i'ccfls 

 of a horfc chefnutj the btan, and other 

 ])lants, when vegetating at rell, that tiie 

 vellelsand fibres on the undi'r tide of the 

 gcrmtn invariably elongate inucli more 

 rapidly than thole on its n[)pcr tide : and 

 thence it follows that the point of the 

 germen mult always turn upwards. And 

 (he adds) it has l)een proved that iilimi- 

 lar incrcafc of growth takes place on the 

 cxtemid tide of the gcrnien when the fap 

 is imiicUed there by centrifugal force, ^ 

 it is altracted by gr.ivitation to its under 

 iide when the feed germinates at reft. 



" 'i'his incrcafcd elongation of tli.e 

 fibres and vclfels of the under iide is not 

 confined to the gennens, nor e\cu to the 

 anminl Ihoots of trees, but occurs and 

 produces the molt extcniivc <-lYects in tlic 

 Aibri(|nent giowth of their trunks and 

 bnmciies. 'J'he ininiediutc efl'ect of gra- 

 vitation is certainly to occwlion the fur- 

 ther dcprefiion of every branch which 

 extends horizontally from the trunk of 

 the tree; and when a young tree inclines 

 to either iide, to incrcafc tliat inclina- 

 tion : but it, at the fame time, attracts 

 tlu: fap to the under lide, and thus occa- 

 lions an increafed longitudinal exlenlion 

 of the fubltance of the new wood on- 

 that lidc. The dcprefiion of the lateral 

 branch is thus prevented, and it is e\ en 

 onnblfd to raile itfelf aljo\e its natural 

 level when the branches above it arc re- 

 moved ; and the young tree, by the fame 

 Jiieaiis, becoaii;b more uprii;!it, in direct 



oppofition to the immediate ai^tion of" 

 gravitation : nature, as ufual, executing 

 the molt important operations by the 

 moft limple means." 



Mr. Knight next proceeds to anfwer 

 objections of which the molt important 

 is, that few branches rife perpendicu- 

 larly upwards, and that roots always 

 fpread horizontally : to this he replies. 



The luxuriant Ihoots of trees which 

 abound in fap, in whatever direction 

 they arc firll obtruded, ahnoll nnitbrmly 

 turn upwards, and endeavour to acquire 

 a particular direction ; and to this their 

 points will immediately return, if they 

 arc bent downwards during any period of 

 their growth; ilioir curvature upwards 

 being occali.med by an increafed I'Xten- 

 fion of the libres and velVels of their uiw 

 der-lides, as in the elongated germens of 

 feeds. The more feeble and llender 

 Ihoots of the fame trees will, on the cou- 

 trarv, grow in ahnoll every direction^ 

 )trobabivbecauie their fibres, being more 

 dry, and their velVels lefs amj.ly fupplied 

 with fap, they are lets alFcctcd by gravi- 

 tation. 'Jheir points, however, gene- 

 rally thew an inclination to turn upwards, 

 but" the operation of bght, in" this cafe, 

 has been pro\ ed to be veiy conlidcrable. 



The radicle tapers rapidly as it dc^ 

 fccnds into the earth, and its lower part 

 is nuich comprelVed by the greater Ibli- 

 dity of the mould into which it pene- 

 trates. The true fap nlfo continues to 

 delcend from the cotyledons and leaves, 

 and occafions a continued increafeof the 

 growth of the upper parts of the radicle, 

 and this growth is fubl'e'iuently augment- 

 ed by the cftecls of motion, when the 

 germen has rifen above the ground. Tlie 

 true fap is therefore neceUarily obfiru.cted 

 in its defcent; numerous lateral roots 

 arc generated, into which a portion of 

 the defconding fap enters. The fub- 

 ftauce of tluf'e roof-, like that of the 

 llender horizontal branches, is lelis fuc- 

 eulcnt than that of the radicle firlt emit- 

 ted, and they arc in coufequcnce lefs 

 obedient to gravitation ; and meeting leis 

 reliltance from the luperficial foil than 

 tnim that beneath it, they extend hori- 

 zontally in e\ery direttion, growing with 

 moft rapidity, and producing the greatcft 

 number of r;unifications, wherever they 

 find moft wannth, and a foil belt adapt- 

 ed to nourllh the tree. As thcfe hori- 

 zontal or lateral roots furround the bale 

 of the tree, the true fap dcfcending 

 down its bark enters ahnoll excluflvely 

 into them, and the firlt perpendicular 

 root, having executed its oltlee of fecur- 



