TRANSACTIONS OF SECTION D. 699 



In the two following cases results were obtained which appear to be at 

 variance with the preceding ; in both of them the percentage of sugar present in 

 the mixture of leaf-extract and distilled water was greater than that in the mixture 

 of leaf-extract and starch-solution. 



Rheum hybridum (extract strongly acid, digestive period 24 hours) : — 



Dextrose 

 c.c. c.c. per cent. 



No. 1.— 50 leaf-extract + 50 starch-solution . . gave -1587 



„ 2.— 50 „ + 50 distilled water . . „ -2702 



„ 3.^50 starch-solution -f 50 „ „ . . „ mere traces 



Daucus carota (extract slightly acid, digestive period 4 hours ; the whole 

 experiment was completed in a single day) : — 



Dextrose 

 c.c. c.c. per cent. 



No. 1. — 50 leaf-extract -f 50 starch-solution , . gave -1052 



„ 2.— 50 „ -t- 50 distiUed water . . „ -12.50 



„ 5. — 50 starch-solution -f 50 „ „ . . „ traces 



„ 4. — 50 leaf -extract (6£«Ze<?) -f 50 starch-solution , , ,, -0847 



„ 5.— 50 „ „ -f 50 distilled water . . „ -0800 



It is probable that in these cases the starch-solution added to the leaf-extract 

 (No. 1 in both) was not in the least degree attacked. The peculiarity to be 

 accounted for is the large amount of sugar present in the diluted leaf-extract 

 (No. 2 in both). It is clear, in the case of the carrot, that the amount of sugar 

 originally present in the leaf-extract (see Nos. 4 and 5) was about '08 per cent. ; 

 the excess of sugar in No. 2 (about '045 per cent.) appears to be due to the action 

 of the diastatic ferment vpon stm-ch contained normally/ in the leaf-extract. The 

 presence of added starch-solution (Carrot, No. 1) appears to have actually impeded 

 the action of the ferment upon the leaf-starch already present. 



The experiments were carried on from the end of June to the middle of 

 August, 1891. 



The author is aware that various points connected with this research require 

 more complete investigation; he is, however, unable to continue the work at 

 present, but hopes to return to it next year. The foregoing facts will, he 

 believes, suffice to prove that Wortmann's conclusion as to the absence of diastatic 

 ferment from green leaves, or its unimportance, is based upon insufficient evidence. 

 It may be objected that the amount of ferment-action indicated in the foregoing 

 experimental results is very small, but much weight cannot be attached to this 

 objection. What the results really indicate is that the amount of diastatic 

 ferment which can, at any one time, be extracted from a leaf is small ; but doubt- 

 less the secretion of the ferment goes on continuouslj-, so that the total ferment- 

 action in, say, the course of a warm night would be very considerable — quite 

 sufficiently so to account for the conversion of starch into sugar which actually 

 occurs, without the direct intervention of the living protoplasm. 



As a conclusive piece of evidence in support of his view, Wortmann cites an 

 experiment which shows that if a leaf be kept in an atmosphere of COo, the starch 

 which it contains is not converted into sugar ; and he infers that this is due to an 

 arrest of the action of the protoplasm upon the starch in consequence of the 

 absence of free oxygen. It appears to the author that this inference is not the 

 true one to be drawn from the fact as stated : a more satisfactory explanation would 

 seem to be that, in the absence of free oxygen, the secretion of diastatic ferment by 

 the protoplasm is arrested, and that it is on this account that the conversion of 

 starch into sugar does not proceed. 



The author desires to acknowledge the valuable help which he has received in 

 this work from Mr. Manley, Assistant in the Chemical Laboratory of Magdalen 

 College, Oxford. 



