Of the Roots of Plants. 239 
It is therefore necelfary that the ftalk ledrefs or reitify 
itfelf in all the other fituations, in order to find its way 
out of the ground : but what force is it that effcits this 
change, which is certainty a violent ailion ? Is it, that 
the ftalk finding a lefs load of earth above it, goes na¬ 
turally that way where it finds the leaft obftacle ? were 
it fo, the little root when it happens to be uppermoft, 
rauft for the fame reafon follow the fame direibion, and 
mount on high. 
Therefore M. Dodart fuppofes the fibres of the fta'ks 
are Gf fuch a nature, as to contrail and fhorten by the 
fun’s heat, and lengthen out by the moifture of the 
earth; and on the contrary, that the fibres cf the roots 
contrail: by the moifture of the earth, and lengthen by 
the heat of the fun. 
Then when the root of the plantule is uppermoft, the 
fibres which compofe one of the branches of the root, are 
not equally cxpofed to the moifture of the earth ; the 
lower part is more expofed to the upper, which muft 
therefore contrail the moftj this contraction is again 
promoted by the lengthening of the upper, whereon the 
fun aits with the greateft force; confequently this branch 
of the root muft recoil towards the earth, and infinuating 
through the pores thereof, get under the bulb, &c. 
By inverting this reafoning, it will appear, how the 
ftalk comes to get uppermoft. 
In a word, we may imagine, that the earth attracts 
the root to itfelf, and that the fun contributes to its 
defcent; and, on the contrary, that the fun attracts the 
ftem, and the earth in fome meafiurc fends it towards the 
fame. Again, 
M. de la Hire imagines, that the root draws a coarfer 
and heavier juice, and the ftem and its branches a more 
volatile one; which difference cf juices, fuppofes larger 
pores 
