Oenothera Lata. 407 



are evidently only useful to the parasites in quite a gen- 

 eral way. The virescence of Lysiiuachia vulgaris, which 

 is occasioned by a Phytoptns, affords perhaps the most 

 beautiful example of a complete series of transitions from 

 flowers to leafy branches.^ This change is obviously the 

 object of the stimulus given by the Acarine and it ob- 

 viously does not matter whether the number of the 

 changed petals of the corolla varies or not. Neverthe- 

 less these and other monstrosities accompanying the vi- 

 rescence are by no means rare. 



The case of the virescence on the galls of Anlax 

 Hieracii, in the flowerheads of Hieraciiim viilgatwn, H. 

 tanhellatiim, etc., which have been studied by Treub, is 

 very instructive.^ These galls are usually situated in the 

 stems far away from the flower, but in rare cases they 

 occur in the flowerhead itself. When this happens the 

 flowers are affected by a whole series of the most re- 

 markable malformations which begin by the calyx pro- 

 ducing little green sepals. These changes are obviously 

 of no use to the Cynipids which live inside the galls ; 

 for the Aidax larvae grow just as well if no inflorescences 

 are borne on the galls. 



Galls not rarely evoke monstrosities of this kind, 

 provided of course that the potentiality for these mon- 

 strous growths already exists. I have found, for ex- 

 ample, a stem of Hieraciimi vulgatiim which was normal 

 below the gall but, above it, was broadly fasciated. In 

 the summer of 1887 I saw several stems of Enpatoriiim 

 cannahmum bearing, about their middle, galls of Pter- 

 ophorns rnicrodactyhis : below these the leaves were green 



^ A. B. Frank, PUanzcnkrankheitcn, 1880, p. 691. 



^ M. Treub, Notice sur Vaigrette des Composccs. a propos d'linc 

 monstruosite de rHicracium iimbcUatum, Archives Neerlandaises d. 

 sc. phys. et nat., T. VIII, p. i and Plate I. 



