INTERNATIONAL BOTANICAL CONGRESS. 191 
twofold and contrary property, such as pertains also to white light, 
and which produces the green colouring-matter of leaves or bleaches 
them, according to its intensity. It is these, also, which change the 
colouring matter of flowers when it has been dissolved in water or 
alcohol.* Those rays called chemical, such as violet, and the invisible 
rays beyond violet, according to recent experiments, confirmatory of 
those of ancient authors—those of Sebastian Poggioli, in 1817, and 
of C. M. Guillemin—have but one single well-ascertained effect, that of 
favouring the bending of the stem towards the quarter from which they 
come more decidedly than do other rays; yet that is an effect perhaps 
more negative than positive, if the flexure proceeds, as many still 
believe, from what is going on on the side least exposed to the light. 1 
e effect upon vegetation of the non-visible calorific rays at the 
other extremity of the spectrum have been but little studied. Accord- 
ing to the experiments we have on this subject, they would appear to 
have but little power over any of the functions; but it would be worth 
while to investigate further the calorific regions of the spectrum by 
employing Dr. Tyndall’s process, that is, by means of iodine dissolved 
in bisulphide of carbon, which permits no trace of visible light to pass. 
How interesting it would be to make all these laboratory experi- 
ments on a large scale! Instead of looking into small cases, or into 
a small apparatus held in the hand, and in which the plants cannot be 
well seen, the observer would himself be inside the apparatus, and 
could arrange the plants as desired. He might observe several species 
at the same time, plants of all habits, climbing plants, sensitive plants, 
those with coloured foliage, as well as ordinary plants. The experi- 
ment might be prolonged as long as desirable, and, probably, un- 
looked-for results would occur as to the form, or colour of the ipe 
partieularly of the leaves. 
Permit me to recall-on this subject an experiment made in 1853 by 
Professor Von Martius. It will interest horticulturists now that 
plants with coloured foliage become more and more fashionable. M. 
* Sir John Herschel, Edinb. Philos. Journ., January, 1 
Pos 8. Poggioli, Biger Scientifici; quoted by Dec, Compt. Rend. 
ues father bart? a nd rpa explanations, founded on the notions 
of Dutrochet, of the existence of a deoxidizing power on the brightest side, 
preg upia tie ii = kelpaa indigo, nd violet rays the eat least ro? 
(C! =e Che aise powerful in 
5 Gers Auzeigs, München 2d Des 1853. 
