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Sydney H. Vines. 
growth of roots — and he accounts for it by means of the foregoing ex- 
planation. 
There exists then a mass of facts relating to the growth of vegetable 
Organs, the whole of which can be explained by the theory that growth 
is gradually retarded by the action of light. Nevertheless, the daily 
periodicily exhibited by the growth of leaves, more particularly those of 
Monocotyledons, has received another explanation. In a paper recently 
published Stebler ') argues that the periodicity observable in the growth 
of leaves is due to the action of light only in so far as this action affecls 
the process of assimilation, or as he puts it, the maximum rapidity of 
growth occurs during daylight whilst assimilation is most active, and the 
tninimum occurs when assimilation is no longer laking place. 
In examining the correclness of Stebler’s conclusions, it will be well 
to enquire what are the premises upon which his reasoning is founded, 
and what experimental evidence exists which would warrant their accep- 
tance as general principles. 
The conclusion arrived at by Stebler, which has been quoted above, 
suggests that the growth of leaves is immedialely dependent upon the 
products of their own assimilation. This idea is by no means a new one. 
It appears to have suggested ilself originally to De Saussure * 2 ). In one 
experiment he grew peas in a closed space over quicklime and found 
that, when the apparatus was exposed to sunlight, the plants died on 
about the fifth or sixth day, and that the air in the receiver contained 
only 16 % of oxygen and apparently no carbonic acid al the close of the 
experiment. When, on the other hand, a similar apparatus was kept in 
the shade, the planls grew and each gained, on an average, 371 milligrs 
in weighl in the ten days during which the experiment lasted, and the 
air in the receiver contained, at the close of the experiment, 3 % car¬ 
bonic acid. From this, and from other similar experiments, he concluded, 
that the presence of carbonic acid gas, or rather the decomposition of it, 
is necessary to the growth of the green parts of plants when exposed to 
sunlight, for they die, when this gas is removed. 
Quite recently De Saussure’s experiments have been repeated by 
Coreinwixder 3 j. From the first series of his experiments, performed in 
1869, he arrived at the same conclusion as De Saussure, namely, that 
the leaves of plants, in order to live, must absorb carbonic acid from 
without. A subsequent series of experiments, however, performed three 
years later, in a somewhat different manner, yielded quite opposite results. 
In these latter experiments he used branches of trees of considerable size 
4) Ueb. das Blattwachsthum. (Jaiirb, für wiss. Bot. Bd. XI. Heft I. 4877.) 
2) Recherches chim. sur la Vegetation, deutsch von Voigt, p. 34 JT. 
3) Comptes rendus. 4 876. 
