THE GROWTH OF THE AXILLARY SHOOTS 



133 



apical nodes, the formation of shoots in the whole stem is inhib- 

 ited, but if the size of the two leaves is sufficiently reduced the 

 stem may form two shoots (Fig. 3 07); the shoots, however, 

 do not grow out from the axil of the leaves but in the node below. 

 The inhibitory effect of the leaf on the growth of its axillary bud is 

 therefore greater than the inhibitory effect on the growth of the 

 anlagen below; but it is, perhaps, not greater than the inhibitory 

 effect of an apical leaf on the formation of a shoot in the second 

 node below the leaf and on the same side of the stem as the leaf. 

 The question is, under which conditions is it possible to cause the 

 growth of a shoot in the axil of a leaf without removing the 

 latter? This can be done by selecting a large leaf and cutting off 



Fig. 108. — Axillary shoots are formed when the stem is short and the leaf large, 

 but not when the leaf is reduced in size. Nov. 15 to Dec. 12, 1923. 



the whole stem with the exception of a small piece, with no other 

 bud except that in the axil of the leaf. When the leaf is small, 

 the chance of a shoot growing out from the axil of the leaf is 

 smaller than when the leaf is large. In the experiment in Fig. 

 108 a small piece of stem with one node and a pair of leaves was 

 split longitudinally. One leaf remained intact, the other was 

 reduced in size. Only in the axil of the large leaf was a shoot 

 formed. This experiment yields the same result when the leaves 

 dip into water and when the stems are in air. 



In this case the inhibition of the growth of shoots can be neither 

 due to an inhibitory hormone sent out by the leaf nor to any 

 increase of growth in the stem due to the leaf; since in either case 

 the inhibitory effect of the leaf on the growth of the axillary shoot 

 should increase with the size of the leaf. 



When the stem is large the chances of the axillary bud growing 

 out are also smaller than when the stem is small. 



