INrLTJENCE OF EXTERNAL CONDITIONS ON GROWTH 



231 



Neliubov^ 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 



Fig. 109. — Formation of mucor-yeast in an oxygen-free medium. 



A B 



Fig. iio.—Impatiensplatypetala; A, in normal atmosphere; B, in atmosphere rich in carbon 



dioxide. 



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 Laboratonumsluft. 

 Ber. Deutsch Bot. Ges. 29: 97-112- 19". 



