232 Transactions of the Royal Canadian Institute 



The effect of foliage, as indicated above, is to deflect the water 

 proceeding from the roots, thus menacing the supply to the upper parts 

 by producing negative pressure in the stems. If so, it was argued that 

 the amputation of the leaves at the moment when cessation of growth 

 becomes manifest should result in increased growth rates. This was 

 the case, as indicated by the following changes in rates: 

 Jy. 9. Leaves cut off at 13.43 hr. From -.3 to .2 mm. per hour (in 20') to .4 mm. (in 20')- 

 Jy. 10, begmning with 7 hr. reading: 



Min.: 60 48 27 30 35 20 Leaves removed 20 30 30 60 



Rate: 42 25 -29 36 26 -60 at 9.40 hr. 30 10 50 40 



or from -.9 mm. per hour (in 20') to .4 mm. (for 20')- 

 Jy. 16, beginning with 9 hr. reading: 

 Min.: 12 25 10 16 Leaves 10 19 



Rate: -25 -7 30 11 removed 42 11 1 



or, from .1 mm. to .6 mm. per hour in 10', and then to 1.5 mm. in 19'. 

 Aug. 13, beginning with 7 hr. reading: 



Min. : 60 60 60 60 60 60 60 40 Leaves removed 20 60 60 



Rate: 15 10 10 o -10 5 15 18 at 13.40 69 45 60 



or from .25 mm. to i.o mm. per hour. 



The amputations were done when the amount and direction of 

 growth were sufficiently apparent in the behaviour of the writing point 

 of the lever that any result of the experiment would be at once apparent. 

 Within a few minutes in all cases it could be seen that the alteration of 

 direction had taken place practically at the moment of amputation. 

 The fact that such was the case is of more importance than the actual 

 rate values for a period previous to and following the amputations. 



The opposite result, as one would expect, follows the reduction of 

 the vascular tissue of the chief stem. The effect is, however, somewhat 

 unexpectedly transient. On September 9th, at the close of the first hour 

 of active growth, at 13 hour the tissues of the basal intemode were cut 

 through sufficiently to reduce the amount of vascular tissue to one fourth. 

 Growth was at once affected (September 9th, fig. 11) there being a total 

 shrinkage of about 0.4 mm. within an hour, after which the growth rates 

 characteristic of the time of the day were resumed. One may recall 

 that the excision of tissues in this manner is not effective in bringing 

 about abscission, even though it is clear that the negative water tensions 

 in the plant are certainly known to be a cause of it (Lloyd, '14, 'i6a). 



Just as increase of growth rates may be induced by the amputation 

 of the leaves, so also by the interposition of shade, not, as will be shown, 

 as a direct result of the reduction of light, but by lowering the rate of 

 evaporation and of transpiration. On days of bright sunshine (July 6th, 

 8th, nth) when the rates were low, these rose to marked positive values 

 when shade was su pplied, and fell again when, after an hour, the shade 

 was removed. 



