1910.] 



Vegetable Asshnilation and Respiration. 



443 



portion of the stalk of each was at once removed under air-free water. 

 Parallel readings with the hygroscope made on these and on two similar 

 attached leaves at intervals during several hours of intermittent sunshine 

 showed no differences that could be attributed to detachment. 



Also, observations made at the beginning of September, 1909, on attached 

 leaves gave readings nearly approaching those obtained with the same 

 hygroscope on the attached leaves of Expt. 5, though the conditions were 

 less favourable. 



These observations do not support the assumption that attached leaves 

 of H. annuus are at a disadvantage compared with detached leaves. I 

 conclude, therefore, that so long as attached leaves of this plant present 

 a fully turgid appearance, they assimilate at an equal rate with turgid 

 detached leaves. 



The Occurrence of Translocation. — On these grounds, and fi'om a study of 

 the details of Sachs' experiments with H. annuus, and those of Brown and 

 Morris, it seems to me certain that the differences which have been found 

 between the rates of increase of attached and detached leaves under the same 

 conditions of illumination are due not to any great extent to differences in 

 the stomatal apertures of the leaves, but chiefly to translocation ; and that 

 the rate of translocation may approach the value which Sachs assigned to it. 



This conclusion cannot be extended to other leaves without experimental 

 evidence. In fact, my Expts. 7 and 8 with Gatalpa tell rather against 

 than for the occurrence of translocation there. Even for H. annuus it must 

 be remembered that the conclusion deals with average results obtained from 

 experiments lasting a number of hours, and leaves quite open the question 

 whether translocation is practically continuous or whether it only begins 

 after a considerable quantity of reserves has been stored up.* 



Broods' Experiments with the Sugar Beet.f 

 In connection with these questions of stomatal aperture and translocation, 

 some remarkable results obtained by Broocks are well worth attention. By 

 means of the dry-weight method he carried out some very laborious experi- 

 ments on leaves of the sugar beet, with the object of investigating the rate 

 of assimilation from hour to hour during the day. He took the control half- 



* Miiller describes an experiment with attached leaves of H. annuus, the results of 

 which show a uniform increase in weight at the rate of about 10 milligrammes per hour, 

 continuing from 7.30 a.m. to 5.30 p.m. ('Jahrb. f. wiss. Bot.,' 1904, vol. 40, p. 468, 

 Expt. 30). This suggests that translocation is continuous in the case of this leaf, and 

 proceeds concurrently with assimilation. 



t Broocks, W., " Uber tiigliche und stiindliche Assimilation einiger Kulturpflanzen," 

 ' Inaug.-Diss.,' Halle, 1892. 



