a 
354 BOTANICAL GAZETTE [NOVEMBER 
lateral runner issues from the side of the shoot with the bud at 
the tip in an erect position. But the bud does not stand freely 
exposed above the general surface of the runner stalk. The region 
immediately behind the bud, where the scale and cauline tissue 
are fused, thickens vertically, so that the bud receives the support 
of the adjacent tissue for its whole height, and is therefore not 
subject to transverse strain tending to invert it upon its base. 
In the absence of supporting tissue for the height of the bud, 
the elongating runner would tend to advance the base of the bud 
<= 
Fic. 4.—Evolution of Erythronium type of runner: 1, normal bud, terminating 
stem (Allium); 2-4, hypothetical stages, with horizontal stem; 5, anatropous bud 
of Erythronium runners; dotted lines and arrows indicate zone of elongation 1n each 
beyond the rest of the bud, as in no. 3, since the unsupported parts 
of the bud would be retarded by friction in passing through the 
soil. The tendency under such conditions would be for the adjacent 
surfaces of the bud scale and the stalk to fuse, as suggested 1n 
no. 4. Up to this point the scales of the bud have taken no part 
in the elongation of the runner or of the bud at the tip; but with 
the fusion of the bud with the surface of the runner stalk, either the 
zone of elongation must shift to a point outside the fusion region, 
or the scales must be included in the growing zone; otherwise the 
tissues would be under continued but irregular strains. In the 
