264 



PHYSIOLOGY OF GROWTH AND CONFIGURATION 



many cases by slightly increasing the carbon-dioxide content of the 

 atmosphere.] 



Neliubov 1 has shown that the form of plants is influenced by the presence of 

 very small amounts of illuminating gas in the air about them, but especially by 

 ethylene and acetylene, which are present in illuminating gas. The shoots 



Fig. hi. — Pea seedlings grown in darkness; I and III in laboratory air containing illumin- 

 ating gas, II in the same air with the poison gas removed. {After Neliubov.) 



A B 



Fig. 112. — Effect of ether upon the flowering of lilac. All shoots excepting the fifth 



from the left (as seen in .4) were treated. The untreated shoot is seen unaltered in B, where 

 the others are all in full leaf and flower. 



grow erect in an atmosphere without illuminating gas, but when even very min- 

 ute traces of this gas are present they bend and assume a horizontal position 



1 Neljubow, D., Ueber die horizontale Nutation der Stengel von Pisum sativum und einiger anderen 

 Pflanzen. Beih. Bot. Centralbl. 10: 128-138. 1901. Idem, Geotropismus in der Laboratoriumsluft. 

 Ber. Deutsch. Bot. Ges. 29: 97-112. 1911. 



