19t0] BLODGETT—BULBS OF ERYTHRONIUM 355 
runners of E. americanum the structure sketched in no. 5 is present. 
The zone of elongation is close to the organic base of the bud, 
while the bud scale is fused for its full height with the stalk of the 
runner. There are no disruptive strains in this case, for the 
external scale of the bud elongates as fast as does the cauline tissue 
of the runner; that is, the scale leaf, like a foliage leaf of the same 
plant (RoBERTSON 17), elongates in the basal zone; the stem 
elongates in its apical region, and as the two are folded back upon 
each other, the two growth regions are continuous about the 
inclosed bud. The position of this region of elongation is indi- 
cated by the space between the diagonal dotted lines in no. 5. 
The cauline tissue in the runner is represented by the vascular 
bundles which unite the terminal bud in the runner tip to the base 
of the parent bulb. The presence of foliar tissue on the same side 
of the runner is indicated by the course of the vascular bundles, 
which turn backward at the base of the scale, and supply the inner 
face of the axial wall of the dropper in the same manner as the thin 
abaxial wall, where there is no tissue other than the scale. (Cf. 
text fig. 1.) 
The runner habit 
The plumule (stem apex) in the cotyledonary sheath does not 
form any bud scales which might by their elongation produce the 
dropper; but the walls of the cotyledonary sheath elongate after 
the primary root is established, and develop the dropper with 
the plumule as the terminal bud therein. This appears to be 
Constant for all the species of the genus. In the subsequent 
Stages in the several western species, and in E. albidum and E. 
mesochoreum, the main stem apex is thrust out as the runner bud 
within the elongated sheath formed by the clasping petiole. This 
Ss exactly comparable to the dropper of the seedling, in that the 
bud is carried forward passively and contributes nothing to the 
development of the structure. In the case of the second runner of 
: dlbidum and of each of the three runners in E. americanum, the 
Tunner is formed by the bud itself forming the runner sheath by 
the elongation of its outer scale. The development of this type 
of runner introduces a new structure into the series present in 
the life cycle of the other species, and the degree to which this 
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