INDUCTION, DEVELOPMENT, AND HERITABILITY OF FASCIATIONS. 9 



capsules of O. grandiflora are Mompha brevhntclla, known at one time as 

 Laverna cenot/iercevorella, and in May and ag-ain in July the insects are 

 constantly invading- the tips . The slightest irregularity in the arrangement 

 of the young leaves during or just preceding the flowering period, an 

 appearance like that shown in plate iii, fig. 2, or such as might result from 

 some external mechanical interference, indicates that the tip when sectioned 

 will prove to be fasciated or bifurcated. There is no sign externally of the 

 fasciated outline in these tiny tips, merely reddish color, inequality of 

 development, or a tiny aperture suggesting a callus. Microscopical exam- 

 ination proves rin.g-fasciations and protuberances to be abundant, and simple 

 fasciations occasional. The development at this stage covers less than 

 5 mm. of the stem, but is none the less perfect. Two such apices are 

 diagrammed in plate v, figs. 10 and 13. In many tips are found long, needle- 

 like incisions, illustrated in plate v, figs. 11, 12, and 13, as if made by an 

 ovipositor. About these the cells have hypertrophied, and cylindrical meri- 

 stems are forming. Throughout the stems at intervals are small areas 

 surrounded by hypertrophies and meristematic conditions (plate v, fig. 15). 

 These are akin morphologically to the meristems in the pith of the old 

 rosettes, and are like those about the track of the larvae in stems in which 

 the pith is infested with the latter. All of them are readily recognizable 

 because of the pun^lish intercellular secretions, seen in plate v, figs. 11, 

 12, 14, 15, and the changes are those which customarily follow in the 

 neighborhood of dead cells. Tips of this appearance collected July 27, 

 1906, were bifurcated, if not definitely fasciated; none of them were normal; 

 and there were "stings" of various sorts in them all. 



The anatomical structure of rings and grooves and of the protuberances 

 proves them to be variations of a single type, for the essential features of 

 their development are the same. The protuberance varies so greatly in 

 its structure and in its morphology that its simplest form is a mere callus 

 associated with a few irregular bundle-elements projecting from the side 

 of the stem (plate iii, fig. 4, and plate v, fig. 10, k). It is easy to conceive 

 cases in which the injury is so small as to be impossible of detection. 

 Incisions in young meristems are quickly obliterated by the turgidity and 

 growth of the surrounding cells (plate v, fig. 12), and it may be assumed 

 that many fasciations are caused by injuries too delicate to follow in any 

 but the initial stages. Only chance enables one to find such stages, and 

 innumerable tips may be sectioned without avail. To a stimulus of this 

 nature, obscure in its histological effects, the simple fasciations must owe 

 their origin . They occur on the same plants with those more easily detected , 

 and may themselves, when bifurcated, be recognized while comparatively 

 young. Yet the stimulus is slow to produce the abnormal condition, and 

 the irritating cause is concealed before the effect is seen. In a tip of 

 O. biennis which contained an active larva, a group of very small paren- 

 chyma cells had differentiated in the pith. This is the condition that 



