340 



PHYSIOLOGICAL BASIS OF POLARITY. I 



the top of a number of potted plants leaving only one leaf at the 

 apex (Fig. 3). We must also remove the free bud opposite this leaf, 

 since otherwise this bud will grow out and produce the same inhib- 

 itory effect as the removed leaf would have done. In this case the 

 experiment would only be a repetition of the preceding experiment in 

 which two leaves were left at the apex. When, however, we remove 

 one apical leaf with its axillary bud very often the one leaf left at 

 the top suffices to suppress regeneration in the basal part of the stem 



Fig. 3. One leaf left at aptx. Giowlh of shouls in the llrsl node below the 

 leaf suppressed, while the shoot in the second node below the leaf, but on the 

 opposite side of the stem can grow out. 



as completely as if two leaves had been left. If regeneration occurs, 

 it takes place in the highest node on the opposite half of the stem 

 which is the second node below the leaf (Fig. 3). In the first node 

 below the leaf no bud can grow out. I have never noticed an 

 exception to this rule in a normal plant. A possible explanation 

 of this phenomenon is furnished by Fig. 4, where that half of the 

 stem through which the sap from the apical leaf flows to the base 

 of the stem is shaded. Since the buds in the first node below 



