a 
CAL ) 
with leaves; weight: 10,90 gr-HCN: 0,0140 gr; i. e. 0,13 °/ ; 
in 100 internodes: 0,0108 er. 
Resuming, [ am brought to the conclusion that in both species of 
Prunus examined (P. Padus and P. Laurocerasus), when the buds 
open, there appears in the shoots growing from them a steadily 
increasing absolute quantity of HCN-compounds, whereas the percentage 
changes little in the period examined. In this same period at least, 
and at any rate for a great part, these substances appear independently 
of the light. Neither is this prussic acid drawn from the internodes 
directly bearing the buds, and developed the year before. Whether 
it is supplied by more distant organs, or is formed in the growing 
twigs out of other substances, this remains to be shown. 
It is also still a point of research in what form the prussic acid 
is contained in the growing paris. That it is necessary to macerate 
‚the killed organs before the total amount of hydrocyanie acid can be 
distilled off, speaks in favour of the presence of a compound that 
can be split up by an enzyme. Moreover, as the liquid distilled from 
etiolated as well as from green shoots of P. Padus and Laurocerasus, 
has an intense smell of benzaldehyde, it is very probable that these 
organs also contain glucosides of the amyedalin-ty pe. 
Physics. — “Observations on the magnetic rotation of the plane of pola- 
risation in the interior of an absorption band”. By Prof. P. Zeeman. 
1. The difficulties of a complete theory of emission are partly 
avoided in a treatment beginning with the absorption, and this may 
have been the reason why Vorer') has followed this procedure, 
though it must be granted that in his method an explanation of 
the mechanism of the phenomenon as in LorENtTzZ’s theory cannot be 
given ®). In Vorer’s theory the separation of a spectral line by the 
action of a magnetic field is found as the separation of an absorp- 
tion line. 
Some particulars in this separation were anticipated by this theory *) 
and confirmed by experiment *). 
1) Voiet. Wied. Ann. 67, p. 345, 1899. 
2) For a comparison of the advantages of the theories of Lonenrz and of Vota, 
see Lorentz. Rapports, congrés, Paris T. [IL p. 16, 33, 1900. en Phys. Zeitschr. 1 
p.:39, 1899. cf. also Puanck. Sitz.ber. Ak. Berlin, p. 470, 1902, 
5) Vorer. Drude’s Ann. 1, p. 376, 1900. 
4) Zeeman. Versl. Akad. Amsterdam. Dec. 1899, Archiv. Néerl. (2), 5, p. 237. 
