FASCIATION 207 



due to physiological disturbance; but what may be the 

 reason for the physiological disturbance is not yet clear. 



Fasciation, which constitutes a deformity, is due to 

 plants or plant parts growing so rapidly and so close 

 together that they become more or less merged or 

 fused. In consequence, a wide or band-like stalk of 

 several or many dandelion heads grown together carries 

 at the top an oval instead of a circular head of blossoms. 

 Similarly, the California poppy, particularly in a season 

 of abundant rain and moderate temperatures, forms such 

 fusions, several flowers being borne at the tip of band-like 

 merged stalks. The suckers which spring up around the 

 bodies of trees or shrubs may be similarly merged into 

 band-like structures. These occasional fusions or fascia- 

 tions are similar to those which take place in succeeding 

 generations of plants under cultivation. In all such cases 

 such fusions or mergings seem to be due to failure of the 

 plant in one or more of its correlations, growth in one 

 direction becoming unduly rapid or unduly slow, so that 

 the symmetry of the plant ig not maintained and deformi- 

 ties arise which reveal the diseased condition. 



The Living Causes of Disease : Infections. — In 

 considering the living causes of disease, or what may be 

 called infections, one should distinguish at once between 

 the mechanical injury caused by the invading organism 

 and the disturbance of the normal physiological activity 

 of the host. For example, one may puncture a leaf or 

 twig with an instrument of the same size as the ovipositor 

 of a " gall fly " and produce a wound which in ordinary 

 circumstances will promptly heal; but if a similar 

 wound is produced by the fly, which deposits an egg at 

 the bottom of the puncture, it will not promptly heal. 

 A gall will grow around the developing grub. The dis- 

 tinction between mechanical injury and the subsequent 

 reactions of the host to continuing stimulation of the in- 

 vading organism may be illustrated by the following 

 examples : 



