78 
action of leaves states that between June 20 and July 4, when 
the nights were very warm, at sunrise the leaves of Helia 
thus?), Solanum, Nicotiana, Cucurbita, Humulus, Datura, 
Atropa, Phaseolus, Juglans, Vitis, Populus and Aesculus were 
quite devoid of amylum. Quite empty were according to the 
above table the leaves of Boehmeria nivea, almost empty those | 
of Batatas edule and Ipomaea peltata. Special attention i a 
called to Nicotiana Tabacum, which in Sachs’s experime ats 
proved quite destitute of amylum, but at Buitenzorg retainel 
a blue tint. And this notwithstanding the short nights in Europe 
as compared with the long ones in tropical regions. That ie 
temperature cannot in this case be considered as the chief agent t 
is evident, and this receives further confirmation from Le 
fact observed by Sachs, that even in cold nights the leaves 0 
Helianthus, Solanum, Datura, Atropa and Aesculus are quite 
emptied. In such nights however Ampelopsis, Phaseolus ant 
Aristolochia had a small residue left, and Dioscorea, Batatas, : 
Catalpa and Morus even a great deal. 3 
If it is therefore allowable to draw a conclusion from the 
observations in Europe and those in the East Indies, it 
be this, that in Europe under favourable circumstances of t 
perature the leaves lose the whole quantity of their amylum 
whereas in the East Indies they retain greater or smaller q 
tities. Whether or not the structure of the generally coriaceols 
leaves in tropical countries has much to do with this differe 
is not evident, since also in some of the plants marked 
an asterisk, large quantities of amylum were present. 
Increase of the quantity of amylum in the daytime and time 4 a 
ats macimum. By making the iodine experiment at different times 
of day it has become clear to me that not in all plants © 
‘quantity of amylum keeps constantly increasing till @ sho 
time before sunset. Sometimes a maximum is attained un 
earlier and then either remains constant for some hours oF i 
off gradually. Some points are given in the table. 
1) See for the species used the paper cited on p. 1. 
