52S PROF. D. T. MACDOUGAL ON THE GROWTH 0F 
Later, F. Rosen (7) made a special examination of the con- 
ducting tissues, but was unable to find any conditions which 
facilitate the movement of plastic material in one direction and 
not in another. 
Recently, L. Jost (5) has taken up the question as to the 
relation of growth and assimilation, and has also devoted some 
attention to the cause of deterioration of leaves grown in an air 
free from CO,. In his experiments, Mimosa pudica was grown in 
an air free from CO,, and with shoots of Phaseolus multiflorus, 
Acacia lophantha, Oxalis Deppei, and O. lasiandra in darkness. 
The greater part of his work is devoted to the behaviour of 
etiolated plants, and he was able to obtain etiolated leaves of 
normal stature on all the above plants, except Oxalis, by the 
removal of coneurrent buds. Such tests were not made in an 
air free from CO, however. Since etiolation is due to the absence 
of the rays of light, from which the energy of chlorophyll action is 
derived, he claims that * Dunkelstarr” is due simply to the fact 
that the chloroplasts, in the absence of the conditions for their 
functional activity, form substances harmful to the organism—a 
fact to which he attributed the death of leaves in darkness, as 
well as in an air free from CO,. In opposition to Vóchting, he 
concludes that growth is in no direct manner connected with 
assimilation. 
So far as experimental tests have been made, leaves exhibit 
wide divergences of reaction in an air free from CO,, as well 
as in darkness; and the writer has deemed it of the greatest 
importance, as a necessary preliminary to the elucidation of the 
main thesis, that.the conditions upon which these variations 
depend should be accounted for. A comparison of the reactions 
of the species used by myself and others, in an air free from CO, 
and in darkness, has also been made. 
RESULTS or EXPERIMENTS. 
It would not be profitable to reproduce the pages of my note- 
books descriptive of the separate experiments, and only the 
general results of each of the series of tests are given under the 
same of the species concerned. 
The following species have been used in my work, viz., 
Arisema triphyllum, Calla palustris, Hibiscus Rosa-sinensts, 
Lsopyrum biternatum, Justicia sp, Lilium tigrinum, Oxalis 
a 
