NA TURE 



\_May i, 1884 



Effect of Disturbance— -The fact observed by Baran- 

 eizky, that a small disturbance, such as a slight shake, 

 increases the transpiration of the leaves, is also easily 

 seen, and my observations show that in some cases the 

 effect may be very transitory. It need not occur in the 

 use of my instrument, since the plant remains quite un- 

 touched, the only necessary movement being the removal 

 and replacement of a vessel of water to allow the entrance 

 of a bubble. 



Effect of Sudden Diminution of the Evaporating 

 Surface. — I have been astonished to find with what 

 rapidity the rate of absorption diminishes when the 

 evaporating surface is diminished by cutting off a twig 

 from the branch under experiment. 



A branch of Portugal laurel was absorbing (April 10) 

 with great regularity. 



small branch cut 



20 

 20 

 another branch cut off 

 IS 

 17 

 16 

 16 

 16 



•3 o 



14 40 



26 o 



35 o 



When the first branch was removed nearly the whole of 

 the permanent diminution was visible in 35" ; in this case 

 the distance from the base of the branch to the place 

 where the small branch was severed was 28 cm. 



In the second experiment half the permanent effect 

 was produced in 20" ; and here the distance of the cut-off 

 twig from the cut end of the main branch was 45 cm. 



But far more remarkable results were obtainel when a 

 long stem of ivy was used for the experiment. 



A stem of ivy was removed from the tree on which it 

 grew on April 13, and was placed with its cut end in 

 water until the following day, when it was fitted to the 

 apparatus. 1 



April 14 — The rate of absorption remained fairly con- 

 stant from 10.30 to 11.45 a.m., when the first branch was 

 removed. 



Rate of 



ALsorpiio 



II 42 



branch cut off 



29 



45 ° 



15 



46 20 



53 ° 26 



The branch which had been cut off left the main stem at 

 a distance of 13 feet 3 inches from the basal end, so that 

 change in the rate of absorption was transmitted at the 

 rate of o'8S feet per second. 



In a second trial the following results were obtained : — 



1 o 



6 o 



11 30 



'3 o 



'5 



14 o 



15 3° 



18 o 



stem cut 



iS 



17 



15 



"5 



The point at which the stem was severed was 16 feet 

 5 inches from the basal end, so that here a change in 



1 The stem was fixed so that its distal end was seme few feet above the 

 base immersed in water. 



absorption travelled at the rate of i*i foot per second. 

 The same result followed on two other occasions, but 

 here the rates of transmission were slower — 



15 feet 5 inches in 30", 

 9 feet 10 inches in 30". 



In the latter of these two cases the part removed was 

 not a branch of the stem, but a branch belonging to a 

 neighbouring stem which had grown into lateral union 

 with it, so that here the transmission of the change must 

 have taken place laterally from the branch to the stem, and 

 then longitudinally along the latter. 



Effect of partly severing the Branch. — My instrument 

 is well adapted for testing the transmitting capacity of a 

 branch which has been partly cut through. I have been 

 much surprised at the fact that cuts to the depth of half 

 or more than half the diameter of the branch produce 

 practically no diminution in the rate of absorption. Indeed 

 a slight increase is often visible owing to the disturbance 

 which must occur when the branch is cut with the saw. 



A branch of yew '55 inch in diameter was sawn (a) to 

 the depth of '25 inch, (b) so deep that the bridge otwood 

 through which the water had to pass was not more than 

 •1 inch in thickness in radial direction. 



3 26 



34 

 35 

 40 

 47 

 4 3 

 37 

 M 

 40 



43 



Rate of 

 Abs rption 



99 



99 

 . cut A made 



98 

 i°3 

 101 



99 



99 



. cut B made 



100 



97 

 100 

 100 



It was only when the bridge remaining after cut B was 

 narrowed, by sawing on both sides at right angles to the 

 former direction, that the rate of absorption fell. The 

 same thing was shown in another branch of yew, the 

 woody part of which was 10mm. in diameter, and which 

 was sawn to a depth of 8 mm., leaving a bridge 2 mm. 

 thick in radial direction. Even this deep section did not 

 diminish the rate of absorption. With the Portugal laurel 

 the same thing was observed ; and here the possibility of 

 recovery from a temporary diminution in absorption was 

 shown in two cases. 



The branch with its bark on measured 11 mm. in dia- 

 meter, and it was traversed by an excentric cylinder of 

 old brown wood 18 mm. in diameter. 



The following figures give the result of section : — 



[ 1 o 

 9 

 '4 



6 

 89 



35 

 364 



38 

 42 

 48 



55 



Rate of 



Absorption 



18 



18 



CUt A 



. 16 



. iS 



17 



■ 17 



19 

 17 

 18 



cut c 

 9 

 9 



