262 BOTANICAL GAZETTE [October 



had already reported a horizontal nutation of these seedlings, which 

 he explained as autonomic. Rimmer later explained this, horizontal 

 growth as a response to unfavorable conditions, especially lack of 

 moisture in the air. Neljubow found that while this response 

 always occurred in the dark in the laboratory air, it did not occur in 

 the dark in a greenhouse or in the outside air. After determining 

 that temperature and moisture were not factors, he sought the expla- 

 nation in impurities of the laboratory air. He found that laboratory 

 air passed through KOH, Ba(OH) 2 , CaCl 2 , red hot CuO, and finally 

 through Ba(OH) 2 gave vertical seedlings; while similar treatment 

 with the CuO unheated gave seedlings with the horizontal placement. 

 This proved that some impurities (probably some of the constituents 

 of illuminating gas) of the laboratory air, which were oxidized by 

 glowing CuO, caused this peculiar horizontal placement. He later 

 produced the effect with mixtures of illuminating gas. He likewise 

 tested a number of the constituents of illuminating gas. Acetylene 

 produced this nutation, but was difficult to work with, because, on 

 the one hand, a slight increase in concentration killed, and on the 

 other, it rapidly disappeared because of its high solubility in water. 

 One part of ethylene in 1,000,000 of air gave the response, while one 

 part in 4000 killed the majority of the seedlings. He likewise men- 

 tions the fact that various other constituents (benzene, sulfur dioxid, 

 hydrogen sulfid, and carbon bisulfid) of illuminating gas are highly 

 toxic. He makes no attempt, however, to determine the toxic limits 

 of the several constituents, or to learn whether one or several deter- 

 mine the toxic limit of illuminating gas. 



Shonnard (ii) mentions several manifestations of the injury 

 of illuminating gas to trees, and describes an experiment with a potted 

 lemon tree exposed to a flow of i.o7 cu - ft of gas per hour. After 

 eight days he notes the exudation of sap in considerable quantity 

 from trunk and branches, as well as the discoloration and falling-off 

 of the leaves. 



Richards and MacDougal (12) tested the effect of carbon 

 monoxid and illuminating gas upon various seedlings. Carbon 

 monoxid, heretofore considered neutral, was shown to be toxic. It 

 was not so effective as illuminating gas, however, in modifying the 

 rate and amount of growth of root and shoot, in retarding the differ- 



