FUNCTION.] ITS FUNCTION CAUSE OF ITS MOTION. 339 



5. The function of the latex is to nourish the tissue among 

 which it is found. Increase in the layers of wood and bark 

 may be arrested, if by ligatures, or cutting off annular por- 

 tions of the bark, the afflux of nutritious particles from above 

 downwards is stopped. Now the latex is the only one of the 

 fluids in the bark which can have a progressive motion, and 

 it is therefore it which furnishes nutrition. Upon robbing 

 Asclepias syriaca of a great quantity of its milk, it ceased to 

 bear fruit, but it sustained no inconvenience upon merely 

 losing its sap. In fact, the loss of only small quantities of 

 latex injures plants very much. It is the phenomenon of 

 autosyncrasis and autodiacrasis (attraction and repulsion of 

 the globules) which produces assimilation and nutrition. In 

 consequence of autodiacrisis, the molecules of latex escape 

 through the sides of its vessels, to be conveyed to the parts 

 requiring nutriment; while, on the contrary, autosyncrisis 

 brings about the assimilation of the nutritious matter. In 

 proof of which, it is found that the distribution of latex is 

 most abundant in those parts where the greatest increase 

 ought to take place, and that the rapidity of the cyclosis is 

 greatest at the periods of development, the temperature 

 remaining the same. 



6. The cause of the motion may be assigned to heat ; for, 

 when Acer platanoides was exposed to a temperature of 18 

 to 24 centig. ( 2 to 11 Fahr.), the latex ceased to move, 

 but the motion was re-established when it was brought into a 

 warm room : to endosmose ; for water will sometimes cause a 

 renewal of motion when it has stopped : to light; because that 

 agent determines the direction of growth : to contraction, which 

 is the effect of irritability ; not however a contraction with 

 successive pulsations, as in arteries, but by a simultaneous 

 action throughout the whole length of the vessel, whose latex 

 is thus brought into a state of powerful tension. Contraction, 

 however, cannot be the first cause of the motion, for it is not 

 even sufficient to change the direction of the currents. When 

 a vessel has been cut through at both ends, it has discharged 

 all its contents by that end to which the current had been 

 directed, and not by the other. But these are to be regarded 

 as secondary causes only ; the essential cause is the perpetual 



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