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PHYSIOLOGICAL BASIS OF POLARITY. I 



plants one leaf is left at the node below the most apical one. In this 

 case both buds in the most apical node grow out into a shoot giving 

 rise as usual to two small Leaves 1 and 2. While these leaves are 

 normally of equal size, a typical and constant difference exists between 

 the size of the two leaves when one old leaf is left in the node below. 

 Leaflet 1, which has the same orientation as this old and large leaf in 



Fig. 9. The inhibitory influence of the leaf upon an apical bud disappears 

 also when the size of the leaf is reduced. Duration of experiment, Oct. 24 to 

 Nov. 7. 



the node below, is practically always smaller than the other. Leaflet 2 

 (Fig. 8). This difference is intelligible on the assumption that a small 

 quantity of the inhibitory substances from a leaf flows towards the 

 apex of the stem; these substances will reach the young leaf facing 

 the same side of the stem where the old leaf is, while they do not 

 reach the other leaf. When we reduce the size of the old leaf, this 

 inhibitory influence disappears (Fig. 9). 



