745 



from hydrogen, is still injurious to roots. I conclude from the violet gray 

 color in many roots of trees injured by illuminating gas that some of the 

 tars, or the ammonia, carried over in the gas are the injurious factors. For 

 the present, this violet discoloration of the roots may be considered the best 

 indication of the injury even if it is not an absolutely certain one. We must 

 agree with Wehmer^ that such root discolorations occur also in death due to 

 other causes and that often in trees killed by illuminating gas in the soil 

 this characteristic is found only sparingly. The later case is easily explained 

 since only those roots discolor w^hich come in direct contact with the injuri- 

 ous agent and thus cause the death of the tree. The root dying subsequently 

 remains uncolored. 



The different trees and shrubs show a great diversity in their power of 

 resistance to the affect of gases. While in Kny's experiments, for example, 

 the elm died very soon, Cornus sanguinea withstood the poisoning of illum- 

 inating gas without any perceptible injury. An analysis made by Girardin- 

 shows how far the effect of a gas pipe may extend. According to it, the 

 soil at the distance of one meter showed empyreumatic oils and sulfur and 

 ammonium compounds. 



A further example of the different behavior of plants toward illumin- 

 ating gas is given by Lackner^. His observations, however, relate to the 

 effect which the gas is said to exert when burned in the room. Retention in 

 a room where much gas is burned is very injurious to camilleas and azaleas 

 and ivy is said to die at once. On the other hand, palms. Dracaenae, 

 Aucuba japonica and other plants are found to be not at all sensitive to it. 



Richter's experiments* prove that illuminating gas acts arrestingly on 

 the growth in length of bean seedlings and other plants and favors the 

 growth in thickness. It is not true that the amount of carbon dioxid, rapidly 

 increasing by combustion, acts as injuriously on the plant body as on the 

 animal body, as people were inclined to assume^ ; it is rather to be supposed 

 that different products of incomplete combustion of the illuminating sub- 

 stances should be to blame for this. 



1 "Wehmer, C. tjber einen Fall intensiver Schadigrung einer Allee durch aus- 

 stromendes Leuchtgas. Zeitschr. f. Pflanzenkrankh. 1900, p. 267. 



2 Jahresber. iiber Agrikulturchemie Jahrg-. VII, 1866, p. 199. 



3 Monatsschrift d. Ver. z. Beford. d. Gartenbaues in d. Kgl. Preuss. Staaten. 

 January, 1873, p. 22. 



4 Richter, O. Pflanzenwachstum und Laboratoriumsluft. Ber. d. D. Bot. Ges, 

 1903, Part. 3. 



5 We repeat that with otherwise favorable conditions for growth, the presence 

 of carbon dioxid up to a high percentage is useful, since it advances the production 

 of plant substance as shown by the increased elimination of oxygen. According to 

 the investigations of Godlewski ("Abhangigkeit der Sauerstoffausscheidung der 

 Blatter von dem Kohlensauregehalt der Luft" in Sachs' Arbeitfen des bot. Inst, of 

 Wiirzburg, 1873, III, p. 343-70) the optimum for the carbon dioxid content lies 

 tremendously high (5 to 10%) in comparison with the content of the air. In this 

 way is explained the favorable action of hot beds and of the low sunken glass houses 

 of the gardener warmed with horse manure. Here the high carbon dioxid produc- 

 tion of the organic substances, which are being decomposed, is united with the 

 abundant development of heat, weakened light and moist air; i. e. the factors 

 essential for a luxiu-iant leaf growth. But blossom development is promoted, how- 

 ever, since with the increased carbon dioxid content of the air, the blossoms are 

 formed earlier and more abundantly. (Demoussy, tJber die Vegetation in kohlen- 

 saurereichen Atmospharen. Compt. rend. 1904, Vol. 139, p. 883). 



