THE FLOWER CLUSTER IS A MODIFIED BRANCH 



27 



these terms becomes clear. When hereafter he encounters, as he very 

 frequently will, a reference to some organ being modified or transformed, 

 it must never be understood that it was first produced and then changed. 

 The exact meaning is that the change takes place in the direction or 

 exercise of the energy which is to produce the modified structure. 



Modification Produced by Injury. — Such a diversion of energy may be 

 caused by accident, as seen in the so-called "Willow-cone" (Fig. 5), 

 resulting from an injury inflicted by an insect in depositing its eggs in 



8 



10 



Fig. 5. Willow twig with tip transformed into a gall-cone through insect agency. 6. Willow twig 

 after fall of leaves. 7. The same with axillary buds enlarged, in spring. 8. The same with axillary 

 buds developed into (a) female flower-bearing branches, t;, scale (modified leaf) from one of the nodes 

 of "a." 9. Scale with its axillary bud developed into a flower, consisting of a pistil only, u, the stipe; 

 6, the ovary; c, the style; d, the stigmas. 10. Longutidinal section through willow pistil, a, placenta; 

 6, ovule. 



the center of a bud. A portion of the structures, having been originated 

 before such injury, will reach a partial development, but further pro- 

 duction is checked and a distorted product results. 



Bud-scales are Modified Leaves. — In the cases which we shall have 

 to consider the modification dates from an earlier stage and is natural 

 and physiological, instead of pathological, as in the case of the willow- 

 cone. Fig. 6 represents a twig after the fall of its leaves in the autumn. 

 Each bud is seen protected by its lowest leaf, permanently enlarged, 

 and developed into a covering scale. At the base is seen the scar of the 

 leaf in the axil of which the bud was developed. Fig. 7 illustrates the 

 twig in the spring after early growth has enlarged the buds. 



The Flower Cluster is a Modified Branch. — In Fig. 8 (a) the covering 

 scale has fallen, the branch has developed to a length of an inch or so. 



