58 EXPERIMENT STATION. [Jan. 



the treated water greatly exceeded that in the untreated. 

 While only a slight difference was shown in the nnniher of 

 shoots in the normal and treated willow cuttings, 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 cuttings as a direct response to oxygen supply. 

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

 riably more slender than those in the untreated, 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 ]dant 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 t3'pe of re- 

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

 ply. Observations on plants grown under a diiiiiiiishod almos- 

 pheric pressure have given somewhat similar results to those 

 shown by the willow cuttings ; that is, they grow more ra]>i(lly 

 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., 1864, p. 60. 

 2 Schimper's Plant Geography, p. 69. 



