No. 494] FASC1AT10NS OF KNOWN CAUSATION 



side of an organ, may result in the malformation of the 

 adult organ, and, according to Ward, 50 may be proved 

 experimentally by aid of a needle. But the assumption 

 of a mere mechanical injury is not sufficient to account 

 for the presence and shape of galls. The same insect, on 

 different hosts, may produce different galls. Again, two 

 distinct species of gall-insects produce very different galls 

 on the same plant or even on the same leaf. Further, ex- 

 periments to bring about artificially the formation of galls 

 through the injection of different chemicals, have thus 

 far proved unsuccessful. 51 



Among plants of Erigeroti canadensis fasciation ap- 

 pears to be quite common. 52 When, however, among the 

 plants of this fleabane infected by the Cecidomyia a large 

 number, at least 10 per cent., were found to be fasciated, 

 it was but natural to attempt to bring the two phenomena 

 into relation. In some of these fasciated plants the fasci- 

 ation begins within two feet of the ground ; in others, and 

 these form the majority, the fasciation began from '1\ .'■» 

 feet above the soil surface and above the point where the 

 galls occurred on the main stem. But while the non- 

 fasciated plants showed a large number of long side 

 shoots, developed at the expense of the main stem, the 

 fasciated plants did not differ materially from normal 

 plants in this regard. A large number of short side shoots 

 bearing flowers were produced on a fasciated main stem. 

 The most plausible explanation is that in the former case 

 the growth of the main stem was inhibited absolutely and 

 that all the strength went to form side shoots, while in the 

 latter case the growing point was not affected sufficiently 

 to dry up. Instead, growth was stimulated. Whether the 

 action of the galls was of a mechanical or chemical nature, 

 though of great interest in other cases, is of compara- 

 tively little importance here, and for the following 



