3i8 



tion is greater or less according to the amount of newly produced dry sub- 

 stance ; it is smallest in the plants under the bell-jars with potash. Naturally 

 the effect of the bell-jars. i. e., the humidity prevailing under them, is to 

 be taken into consideration. This factor manifests itself, when compared 

 with the uncovered specimens, by the lower percentage of dr^- weight in 

 the plants, i. e., by a loose structure and longer petioles. 



If the specimens from the bell-jars containing pota.-h are compared 

 only with those of the other bell-jars, the result is more certain. The lack 

 of carbon-dioxid manifests itself most by the lessened total production, 

 especially in the leaf apparatus; the upper surface is only about half as 

 large. The most striking effect is the amount of evaporation, which is cal- 

 culated per gram of dry substance present. This is greatest in the plants 

 deprived of the carbon-dioxid supply. The same condition is found in the 

 calculation of the evaporation per square centimeter surface in the plants 

 grown under both conditions. This fact should be associated with the re- 

 sults of other experiments, according to which it is evident that the amount 

 of evaporation increases also in plants which lack other nutritive substances. 

 Tf. for example, plants from a normal favorable nutrient solution are placed 

 in one of too low concentration, or in distilled water, evaporation is in- 

 creased ; it increases also in seedlings after the removal of the organs con- 

 taining reserve food, the cotyledons. It may be assumed that the plant 

 must force itself to a greater transportation of water through its roots, i. e., 

 to a greater one-sided kind of labor, in order to meet lesser amounts of re- 

 serve substances contained in the solution due to their increased absorption 

 by the roots from the surrounding soil. 



For practical work, the above investigations suggest an attempt to in- 

 crease production by increasing the supply of carbon-dioxid. Experiments 

 actually show that a much more rapid formation of starch is obtained by 

 increasing the carbon-dioxid. In many plants an increase up to 6 to 8 per 

 cent, was possible. Of course, a different absolute quantity of carbon-dioxid 

 is necessary for each plant and in the same plant for every other combination 

 of the vegetative factors in order to obtain an optimum production. The 

 strengthening of the vegetative processes by the addition of carbon-dioxid 

 manifests itself in the more compact growth and thicker leaves\ 



While previous experiments have taken up the results of a lack of car- 

 bon-dioxid for the whole plant, Vochting- tested the behavior of various 

 branches, which were left on the normally growing plant, but transferred 

 to an atmosphere free -from carbon-dioxid. It was found thereby that each 

 branch and leaf must be maintained by its own work and that their life 

 activity gradually dies away if this work is prevented by a lack of carbon 

 dioxid. The plant can, indeed, develop further the branches in the atmos- 

 phere free from carbon-dioxid, but the leaves on these branches are a faded 



1 Feodoresco, E., Einfluss der Kohlensaure auf Form und Struktur der Pflanzcn. 

 Cit. Centralbl. f. Agrikulturchemie, 1900, p. 137. 



- Vochting, H., tJber die Abhang-igkeit des Laubblattes von senier Assimi- 

 lationstatig-keit. Bet. Zeit. 1891, Nos. 8 and 9. 



