INFLUENCE OF EXTERNAL CONDITIONS ON GROWTH 



26l 



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 



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



A B 



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



dioxide. 



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

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

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



