V. The Iufluence of Light upon the Growth of Leaves. 
119 
paper by Sachs on the subject of etiolation 1 ) in which it is shewn that 
the excessive elongation of the sletn and the smallness of the leaves of 
etiolated plants are very general, but by no means universal phenomena. 
For example, the leaves of manv Monocotyledons (Tulipa Gesneriana, Iris 
purnila, Albuin Cepa) attain in the dark a greater length than vvhen 
grown in the light, although they are not so broad; and the leaves of 
certain Dicotyledons (e. g. Beta) becoine nearly as large when growing 
in the dark as vvhen growing in the light. It cannot be denied, there— 
fore, that here are instances of the growth of leaves when it was im- 
possible for them to assiinilate. 
The theory of the »self-nulrition« of leaves has already met with 
considerable Opposition. Batalix 2 ), from his experiments upon etiolated 
planls, coneludes that the young leaves develope al the expense of the 
nutriment stored up in the seed, and that it is only when this is exhau- 
sted that their further growth becornes dependent upon the products of 
their own assimilation. Godlewski 3 ) infers from his investigalions of the 
relation existing between the formation of starch in the cblorophyll-grains 
and the proportion of Co 2 present in the air, that the inodifications of 
form observable in etiolated plants are not due to the Suppression of the 
process of assimilatiou. More recently this subject has been studied by 
Rauwbnhoff 4 ). He flnds that leaves are not capable of nourishing them- 
selves immediately after their escape from the bud, and he points out 
that etiolated leaves are not strictly comparable with those which are 
just emerging from the bud, as Kuaüs suggests, for they are vnuch larger, 
and their tissues are more highly differentiated. 
1 may now speak of my own experiments with reference to this 
subject. The various experiments of Kraus and others (with the ex- 
ceplion of those of Godlewski) upon which the different views above- 
inentioned are founded are directed to one side of the question only. 
Darkness is certainly a means of arresting assimilation, but it is not the 
only means, and further, a plant kept in the dark is not only prevented 
from assimilating, but a disturbing element is introduced into many other 
processes such as transpiration etc., the effect of which cannot be elimina- 
ted in the estimalion of the results produced 5 ). It is therefore unjusti- 
fiable to assert that the many differences which exist between the leaves 
of a plant which has been kept in the dark and those of a similar plant 
t) Heber den Einfluss des Tageslichts auf Neubildung und Entstehung verschie¬ 
dener Pflanzcnorgane. Bot. Zeit. 1863. 
2) Bot. Zeilg. Oct. 1871. 
3) Flora. 1873. p. 383. 
4) Over de Oorzaken der abnormale Vormen van in het donker groeiende Planten. 
Amsterdam 1877. 
5) See following paper on Influence of Light on the growth of unicellular organs. 
