540 . PROF. D. T. MACDOUGAL ON THE GROWTH OF 
to carry on the development of the leaves during the first stage, 
i. e. from the rudimentary condition to the unfolding of the 
leaves, without regard to the amount of CO, in the air, unless 
the proportion should be so great as to greatly diminish the 
volume of the oxygen. 
The greatest divergences of reaction appear during the secoud 
or unfolding stage. The leaves of some plants quickly perish at 
the beginning of this stage if in an atmosphere free from CO, ; 
others carry on a more or less complete development before 
perishing; others attain a size somewhat less than the normal, 
and then continue to live in an apparently healthy manner; and 
others attain a natural size, and continue existence showing no 
deviation from the normal. 
Thus Vóchting (10) found that the leaves of Solanum, Tro- 
p«olum, and Mimosa exhibited signs of deterioration in from 
3 to 8 days after unfolding began; and Jost (5) obtained the 
same result with Mimosa, and Arisema exhibited similar re- 
actions in my own experiments. De Saussure (8) found that 
the leaves of Lonicera, Prunus, Ligustrum, and Amygdalus 
began to perish in 12 days. Corenwinder (2) found that leaves 
on a young shoot of Ficus perished after an exposure to an 
air free from CO, for a month, and, later, in an experiment 
with a branch of an older specimen of ZEsculus, obtained a normal 
development. Vöchting (10) found that the leaves of Cardio- 
spermum finally perished in an atmosphere free from CO,, although 
able to attain a normal size ; and in my own experiments Trillium, 
Calla, and Lilium exhibited similar reactions. Godlewski (3) 
found that seedlings of Raphanus were able to form normal 
leaves ; and Vines (9) obtained the same results with seedlings 
of Cucurbita, Ricinus, Phaseolus, and Zea, and with tips of 
branches of Cardiospermum, Dolichodeira, and Helianthus. 
It is to be noted, however, that in this last-named series 
the experiments were carried only through a period of 8 to 10 
days, and that the leaves of the species named were approxi- 
mately equal to those of control plants only. In Véchting’s 
tests Cardiospermum was able to form leaves hardly equal to 
the normal, which soon perished; and in my own tests with Zea, 
divergences from the normal were shown in 10 days and de- 
terioration soon followed. The tests made with Phenix were 
not of sufficient duration to determine the point at which the 
deterioration due to the exhaustion of the food-supply occurs. 
