1920] CRIBBS—TODEA BARBARA 281 



states: "The first bundle, which usually ends blind in the foot of 

 the embryo, curves after a very short course through the stem into 

 the first leaf; from the point of curvature the development of a 

 bundle, which runs out into the second leaf, begins. In the case 

 of the subsequent leaves the same conditions prevail. " DeBary's 

 interpretation of the stelar structures in this group has been 

 supplanted by the theory of the stele as a unit in stem development 

 (Van Tieghem 12), which was strongly supported by Gwynne- 

 Vaughan's (5) work on Primula, and subsequently by others, and 

 which has at present gained most general credence. The conditions 

 found in the young stem of Todea Barbara give evidence in support of 

 the later theory; for, as is readily observed, the trachea group 

 above the foot is composed of 15-25 elements, while the number 

 entering the first leaf is commonly but four, and was never observed 

 to exceed six (fig. 5). 



The stem axis bends at each node in the young sporophyte, 

 so that the traces depart from the outer angles, a behavior undoubt- 

 edly referable to the manner of origin of the leaves, and is caused by 

 pressure of segments cut off from the leaf apical cells and stem 

 apical cells following the isolation of the former in a small meristem 

 which has not yet become closely invested with leaf bases (figs. 35, 

 37). In the early organization of the stem a single apical cell 

 appears, which is usually of the three-sided pyramidal type. 

 Sometimes it is truncated at the base, and in most instances was 

 found to be broader near the middle than at the top (fig. 36). 

 Frequently, however, the apical cell is four-sided in transverse 

 section (figs. 39, 41), and, like that of the root, cuts off segments 

 more or less irregularly, often giving the appearance of a cluster of 

 initials (figs. 38, 46). Only one instance of initials not certainly 

 referable to a single cell was found (fig. 40) . This instance occurred 

 after the organization of the medulla, and appears to be a true 

 case of more than one apical cell; but the earliest meristems were 

 always referable to a single initial. At the level of departure of 

 the first trace there is still a paucity of sieve cells (fig. 5); the 

 pericycle is likewise incompletely developed, and, in fact, the 

 feeble development of all the extra-xylar elements is quite noticeable 

 in contrast with their relative prominence at higher levels in the 



