INDUCTION, DEVELOPMENT, AND UK RITABI LIT V OF F ASCI A TI< )NS. 7 



is represented in fig. 1; a later stage in iig. 1 shows the character of ihc 

 meristematic groups embedded in thick-walled parenchyma, and in tie;. 3 

 the gradual differentiation into i)hloem and xylem is i)ictured. Interme- 

 diate between the ring and the groove types is found an example illustrated 

 in plate IY, series 4, of what is classed by Xestler (<S) in / ". lun^ii'olia as 

 an "imperfect ring." In this the meristems arise in the pith, a ring of 

 bundles develops there, and the ring passes o\vr to one side- until it touches 

 the primary bundle-ring, with which it then fuses. At this point the flat 

 telling of the stem first becomes marked. In one individual the lysigenous 

 cavity, characteristic of the ring-faseiations, formed within the second 

 bundle-ring and passed out into the cortex when the two bundle-rings 

 mended. Stems with the protuberances on the plants of (). cntciata when 

 sectioned (plate iv, series 2) reveal conditions similar to those of the two 

 types preceding. The medullary parenchyma cells in the center of the 

 stem become smaller and more closely crowded together. A meristem then 

 arises in the pith and, after differentiating into a secondary bundle-ring, 

 becomes part of the primary ring, as in the intermediate or ring-groove 

 type. The composite ring then bulges out at the point of fusion, and a 

 portion of it is cut off to form the protuberance. This cylindrical process 

 (plate v, fig. 4) possesses a woody bundle-ring, but there is no apical 

 meristem and, near the tip, primary tracheae and sieve-tubes run irregularly 

 across its axis (plate v, fig. 6). Above this arc irregular, yellowish callus 

 cells (plate v, fig. 5). In a very common variant of its structure, serial 

 sections show, in the pith below the protuberance, a group of cells formed 

 of tracheae and sieve-tubes, which run transversely and in great confusion. 

 As this group passes toward the periphery and touches the primary bundlc- 

 ring the regularity of arrangement is disturbed in the latter, and is only 

 restored after the knob has been entirelv cut off from the stem. In another 



v 



variant the meristem does not appear below the protuberance, nor does 

 the stem fasciate. In a case of this kind the cortex around the main stem 

 was found to be eaten off by insects, the growing region injured, and the 

 lower buds forced out. This is simple abortion of the main axis, with 

 destruction of leaves and buds, which leaves the surface of the aborted 

 stem in the form of a hard and smooth projection. The variations of these 

 regions, of which there may be said to be almost as many as there arc 

 specimens, together with the variations of the rings and grooves, arc all 

 manifestations of the same principle. The early conditions of one arc 

 doubtless similar to the conditions of all, and for this reason special interest 

 attaches itself to the young stages of any of them. 



A young protuberance with accompanying fasciation was found in a stem 

 of O. cntciata, illustrated in plate in, fig. 6, which was cut in September 

 from one of three slow-growing plants which had elongated 20 cm. from 

 the rosette stage. The phyllotaxy was disturbed for 3 cm., and the leaves 



