CHAPTER XIV 



INHIBITORY EFFECTS OF A SECOND ORDER BY AN 



APICAL LEAF 



Aside from the inhibitory effects of an apical leaf on shoot 

 formation in the direct path of the descending sap there exist 

 other small inhibitory effects outside this path. These latter 

 inhibitory effects outside the path of the descending sap from an 

 apical leaf on shoot formation may be called inhibitory effects of a 

 second order to distinguish them from the inhibitory effects 

 which lie directly in the descending path. These inhibitory 

 effects of the second order show themselves in the fact that in 

 stems with one apical leaf even the shoot formation on the side 

 of the stem opposite to that of the leaf is delayed and compara- 

 tively diminished. 



Six short stems with one leaf each at the base (Fig. 90) were 

 put with the base of the stem in water. Each stem formed only 

 one shoot at the apex and roots at the base. The experiment 

 lasted from Dec. 7, 1922 to Jan. 5, 1923; the dry weight of the 6 

 leaves was 2.8998 grams, and the dry weight of all the shoots pro- 

 duced by the stems was 348 milligrams. One gram of leaf pro- 

 duced therefore 120 milligrams of apical shoots. 



Simultaneously an experiment was made with 5 short stems, 

 each of which had a leaf at the apex (Fig. 80 in Chapter XII). 

 In this case 2.607 grams of dry weight of apical leaves produced 

 180 milligrams of shoots in the basal part of the stem, or 1 gram 

 dry weight of apical leaf produced only 68 milligrams of shoots. 

 The difference between the effect of the leaf on shoot production 

 in the ascending and descending sap cannot be attributed to a 

 difference in the dry weight of the stems since the dry weight of 

 the stems in the experiment with the ascending sap (Fig. 90), 

 where more shoots were formed, was only 1.87 grams as against 

 3.9 grams in the experiment with the descending sap (Fig. 80). 

 The only conclusion is that the descending sap sent out by the 

 leaf formed in this experiment per gram dry weight of leaf only 



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