70 White. 



be a fact. On the other hand, there is some circnmstantial evidence 

 that certain of these cases may need the services of a pathologist rather 

 than those of a geneticist in order to determine the nature of their 

 ailment. I have no doubt, that in some instances, the presence of 

 fasciation in woody and herbaceous plants is a strictly hereditary 

 character. In other instances, some of which have come directly under 

 my own observation, I believe the anomalous condition to be due to 

 perennial fungi or to bacteria. I have no other proof than circumstantial 

 evidence for this statement, but several perennial fungous diseases of 

 economic importance, such as those resulting from the presence of 

 several species of Exoascus, are known to be capable of bringing about 

 marked modifications in the character of the host-plant structures. As 

 a rule, they do not affect every individual plant of a group to the same 

 extent on their first appearance, even though these plants may all belong 

 to the same variety. Often only a few branches show the anomaly, 

 the disease in some years gaining, in others, losing ground. Some 

 species of Exoascus produce "witch-brooms", which in the matter of 

 increasing the amount of woody tissue through stimulation, is comparable 

 with what takes place in the production of a fasciated branch. 



c) Uninherited (somatic) form of fasciation. 



De Vries and others regard heredity as a matter of degree. A 

 single fasciated plant appears in a normal culture of a species, and the 

 next year, seed from this plant produces another large culture with 

 perhaps a single fasciated plant or perhaps three or four present. The 

 per cent is small and cannot be increased by selection. It is designated 

 as a poor race. Rich races produce larger numbers of the anomaly. 

 In order to show that the value of heredity as a conceptional term wiU 

 be decreased if a sharp line cannot be drawn between non- inheritance 

 and inheritance of characters, it seems to me necessary to emphasize 

 the importance of this point, and I shall go into greater detail here 

 than the subject would otherwise warrant. Somatic fasciations may be 

 classified under several heads on the basis of difference in causal 

 factors, although these factors, from a physiological standpoint, function 

 in producing the character in the same manner. Fasciations may be 

 caused by insects injuring the young embryonic tissue, by mutilation 

 through the agencies of frosts, higher animals and man by abruptly 

 increasing the supply of nutriment, either by checking the plant's abihty 



