150 THE PLAXT WOKLD. 



the rosette period, and the growing region becomes linear before 

 the time of the elongation. The stems are then flat from the 

 base. If the plant is adult at the time of the invasion the in- 

 juries are in the upper part of stems which have already com- 

 jDleted their first growth. These fasciated stems are round below 

 and flat above. In a given field of plants it will also be noticed 

 that most of the fasciated individuals begin to flatten from the 

 same relative point on the axis. This seems to indicate that the 

 banding is stimulated in all of them at the time of the advent of 

 the new swarm. In an adjoining field, ajiparently of similar 

 character, the failure of a swarm, or its less ])enetrating mode of 

 attack, may account for the abseuee of any degree of fasciation 

 whatever. 



The importance of conditious of culture correlates well with 

 the above observations and the cliaracter of tlie euviroument is 

 significant in the production of the fasciations in two ways; 

 namely, in ]>roviding a favorable habitat for the insect, and in 

 promoting vigor in the individual plant, such that it will recover 

 from, and not succumb to, the mutilations. Degrees of moisture, 

 isolation, and light all influence the activities of the insect as well 

 as the development of the plant itself. Healthy ]dants may be 

 more attractive to the insects; dam]i, or rainy weather may drive 

 the insects into the flowerint;; heads, or under the vouna,' leaves; 

 isolated plants in full sunlight may l)e better exposed for the 

 hatching of the eeo's. An entoiiiolo<>ical studv of the habits of 

 these animals would be of interest in this connection, and would 

 throw light on the exact relation of the insects's life-history to 

 the life-history of the plant. There always reuuiins tlie further 

 necessity that the plant shall be "susceptible," l»ut we are assured 

 by deVries that the degree of susceptibility of the uoruuil, and 

 flourishing ])rimrose is superior to that of the ailing i)lant, and 

 that the physiological responses of the two are not alike. 



The question of heredity in the (Kuotheras is of interest 

 because of deVries' long-contimu'd experiments. lie found fas- 

 ciation to be partially hereditary in several other species, and 

 made some observations on (Euothera. He did not, however, 



