8 INDUCTION, DEVELOPMENT, AND HERITABILITY OF FASCIATIONS. 



abnormally crowded for 1.5 cm. Transverse sections of a growing region 

 revealed callus over the main tip, just above the pith. The procambial 

 strands about the callus seemed unaffected by the injury to the apical 

 meristem and were continuing their activity. Longitudinal sections of 

 a second plant (plate v, fig. 7) showed callus at the tip of the main 

 axis in the former position of the apical cells. Beneath it trachea; and 

 sieve-tubes had differentiated and ran irregularly, many in a transverse 

 direction, across the apex. A section of this stem is seen in plate v, fig. 8, 

 and shows the callus and the apical conditions. The slight depression 

 under the callus is surrounded by a ring-shaped meristem (plate v, fig. 7). 

 The tip has evidently been injured, the meristem has spread in a circular 

 direction, and has become distributed as a ring. As enlargement takes 

 place in the tip of the stem, its apex will project as a protuberance of greater 

 or less development, showing transverse bundle-elements beneath a mass 

 of callus. When unequal growth pushes the callus to one side the ring- 

 splits and the stem becomes flattened. The origin of the injury which 

 induced callus formation is to be found in the surrounding plants. In 20 

 rosettes of O. cruciata next these individuals larva; were feeding', and as 

 the leaves of one of the three in question were freshly eaten, and as another 

 contained a larva within the stem in the lower part, these insects were 

 undoubtedly the agents which attacked the young tips. 



The relation of certain insects to the oenotheras is known to be a constant 

 one, and more than one genus is recognized as parasitic upon them. The 

 forms found in Bedford Park and in the experimental grounds are species 

 of Hfo/np/ia, a tiny grayish moth with spotted wing's. The eggs are laid 

 in the leafy tips and, later, lame are abundant in the apiees, the capsules, 

 and the pith of stalwart plants. They are particularly common in rosettes 

 toward the latter part of the summer, and. as they develop many bind 

 together the leaves to form a shelter and feed among the tender tissues in 

 the winter and again in the very early summer. Most of them eat only young 

 leaves and never reach the meristem; many devour and destroy the apical 

 tissues; while still others irritate or injure them. They are found not only 

 in the rosettes that come from seed, but in those which form in late summer 

 at the ends of old branches to carry over a perennial growth. The fasei- 

 ated rosettes of late summer frequently appear in pairs, and it is common 

 to find callus and inhibition of growth between the two (plate v, fig. 9). 

 The condition of the branch seems to indicate that the main axis has been 

 destroyed and the side-buds injured as they were forced out. Such branches 

 commonly have circular meristems in the pith, surrounding spots of brown 

 discoloration of the sort which develop about masses of dead cells. 



A second kind of injury may arise through the ovipositors of the insects. 

 In the pith of woody stems of O. cruciata, O. parviflora, and O. biennis, and 

 in the capsules of O. grandiflora and other forms, are larva; closely related 

 to those in the rosettes. Those which undergo metamorphosis in the 



