58 EXPERIMENT STATION. [Jan. 



the treated water greatly exceeded that in the nntreated. 

 While only a slight difference was shown in the nnmber of 

 shoots in the normal and treated willow cnttings, the latter 

 showed a greater development. The increased development of 

 the shoots and foliage was correlated with the greater root de- 

 velopment. We regard the increased root development of the 

 treated willow cnttings as a direct response to oxygen snpply. 

 The roots of cuttings growing in the charged water were inva- 

 riably more slender than those in the nntreated, and were also 

 characterized by an early appearance of a profuse growth of 

 secondary roots. 



Effects of Illuminating Gas on Lenticels. 



The lenticels or breathing pores of the willow cuttings grown 

 in water charged with gas showed a marked difference in devel- 

 opment. They always show a greater growth in water, but the 

 development of the parts submerged in water charged with gas 

 was exceptional. Many years ago Nobbe ^ observed when con- 

 ducting water culture experiments with potatoes that the sub- 

 merged tubers developed unusually large lenticels. 



This stimulation of the lenticels was one of the most conspic- 

 uous reactions we observed in our experiments with willow cut- 

 tings, and appears to be a general response to a demand for 

 oxygen. (Fig. 3). The gas in the treated water had prac- 

 tically the same asphyxiating effect on the plant as a decreased 

 supply of oxygen, the demand for oxygen being increased and 

 the plant responding by a greater growth of the lenticels. 



The response on the part of the roots of the willow cuttings to 

 the stimulating effects of gas appears to be the same t^'pe of re- 

 action, i.e., practically amounting to a decreased oxygen sup- 

 ply. Observations on plants grown under a diminished atmos- 

 pheric pressure have given somewhat similar results to those 

 shown by the willow cuttings; that is, they grow more rapidly 

 than those under normal conditions. This is not, however, the 

 effect of the diminished pressure alone, but is due to a diminu- 

 tion of the partial pressure of oxygen. Wider and Jaccard - 

 have demonstrated that the optimum growth of plants does not 



• Landwirtsch. Versuchstation, Vol. IV., 18G4, p. 60. 

 2 Schimper's Plant Geography, p. 69. 



