16 INDUCTION, DEVELOPMENT, AND HERITABILITY OF FASCIATIONS. 
forms found in the Valerianacez, ‘‘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 Valerianacee. 
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 cenotheras the histology of the early stages of development of 
fasciated stems is varied. Many different forms are found related anatom- 
ically to each other and to ring-fasciations. All may occuron 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 fasciated 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. 
