leaves, brought about by the opening of the buds, also in the dark, 
one should know the changes caused by the occlusion of the light, 
independently of the formation of shoots. I properly ought to have 
done the same with the twigs of P. Padus, but nobody will, I trust, 
expect that these organs, with their peridermal coating, should show 
energetical processes of assimilatory kind. 
The experiments with P. Laurocerasus took place not only with 
cut leaves, but also with branches bearing leaves. To examine 
Whether cut leaves should change in the dark their amount of HCN, 
the halves of the freshly plucked organs were cut off along the middle- 
nerve and killed immediately. The other halves, with the middle-nerves 
still adhering to them, were brought in the hot house, and placed, 
under blackened bell-jars, in a glass, the petioli dipping in water. At 
the end of the experiment, the middle nerves were cut off, and the 
remaining halves of the blades analysed. 
It appears that by staying even a fairly large number of days in 
the dark, the leaves undergo no modification whatever as regards 
the amount of HCN, at least not in winter *). 
25 leaves (Noordwyk). 13. 12. O1. 
Halves @ analysed immediately: HCN: 0,0155. 
Halves 4, after staying in the dark till 29.12. 01., HCN: 0,0142 er. 
25 leaves (Noordwyk). 
Halves a: 13. 12. 01., 0,0357 er. HCN. 
Halves 6:95 od 03 10 035 Leer. IEN: 
It follows that even after about one month no change whatever is 
to be noticed. Recently F. F. BrACKMAN and G. L. C. MarrHarr ®) 
have shown that the leaves of the cherry-laurel remain fresh and 
living in the dark even after fifty days. On the other side, the results 
given above quite agree with those obtained by A. J. vaN DE VEN ®), 
using microchemical methods. 
= 
However, after a longer stay in the dark, or even, in certain cases, 
at a temperature of 20° C., after a shorter stay, pathological changes 
become noticeable in the leaves. Yellow spots, originating along the 
middle-nerve and the more important side-nerves, cover by and by the 
surface of the leaf till it becomes uniformly yellow. However, these 
organs don’t die at once; they remain fresh many days, but the 
analysis shows that they lose rapidly their hvdroevanic acid. 
1) J. Corarp: (Journal de Pharmacie de Liège, 2e année, 1895 p. 1) states that 
leaves of cherry-laurel, when the entire shrubs remained in the dark from May 
till August, yielded a percentage of HCN, somewhat inferior to the percentage in 
plants exposed to the light. 
2) Annals of Botany, XV. 1901, p. 553. 
8) Dissertation Amsterdam. 1898, p. 35. Archives Neerlandaises, 1. c. p. 392, 
