16 INDUCTION, DEVELOPMENT, AND HERITABILITY OF FASCIATIONS. 



forms found in the Valerianaceas, "fasciation of side-branches of a slight 

 degree and disarrangement of phyllotaxy." He later says: "All the 

 foregoing anomalies are phenomena of infection and owe their form to the 

 stimulus of a parasite . ' ' Although these experiments were never published 

 in detail, and emphasis was laid on phenomena other than those of fascia- 

 tion, the hypothesis that fasciation was due to infection was evidently in 

 the author's mind. Had he lived longer he might have taken up the sub- 

 ject more specifically and demonstrated it in relation to the Valerianacese. 

 He concludes his article with the following sentence: "I am convinced 

 that many instances which have hitherto been explained as spontaneous 

 variations owe their origin to the activity of insects, although a Phytopus 

 need not always be the stimulus." 



The analogy of the artificial production of fasciation leads one to infer 

 that the insect is but very indirectly the cause, and that the physiology is 

 the physiology of traumatic after-effects. The nature of the changes in the 

 chemical and physical conditions of cells after wounding is as yet but im- 

 perfectly understood, and the enormous hyperplasies resulting from the 

 mechanical irritation of foreign substances, especially those associated with 

 the parasitism of insects, are among the most interesting of unexplained 

 physiological phenomena. 



The following points are to be emphasized in summing up the foregoing 

 statements: 



(1) In the (jenotheras the histology of the early stages of development of 

 faseiated stems is varied. Many different forms are found related anatom- 

 ically to each other and to ring-fasciations. All may occur on the same plant, 

 and the differences between them are morphological, not physiological. 



(2) The fasciations arise through the agency of injuries inflicted upon 

 the growing regions by insects. Bifurcations without definite flattening 

 develop through the same set of stimuli. 



(3) The injuries must be inflicted upon the initial meristem, and can 

 ordinarily be detected only microscopically, and at the earliest period of the 

 ensuing growth. In such cases their course is almost immediately obscured 

 or obliterated by the development of the surrounding cells. 



(4) Injuries may result in the abortion of the whole or part of an axis, 

 or in the formation of small processes on the stem. These malformations 

 are described as "protuberances," and their development is almost invar- 

 iably associated with fasciation or bifurcation, or both. 



(5) Plants infected early in the rosette stage fasciate as rosettes; those 

 infected after the stems have begun to elongate are faseiated only in the 

 upper parts of the branches. 



(6) To secure the greatest number of fasciations, the plants should be 

 given the best conditions for their individual development, and the seed 

 should be planted so that the period of greatest vigor may correspond with 

 the time when they are most sure of infection. 



