TULIP DROPPERS 467 
Between these two extremes the stem and the leaf join as 
contiguous parts of the entire cylinder. The stem part is 
characterized internally by its double row or ring of vascular 
bundles and it is noticeably thicker than the leaf portion. The 
general relation of the bundles is also well shown in such longi- 
tudinal sections as are given in figures 4 and 5. On the 
exterior the stem segment of the dropper is somewhat ridged 
throughout its entire length as is indicated in figure 3 and in 
the drawings of the cross-sections at c, d, e and f. 
The entire bulb of the ordinary non-burrowing plant of the 
tulip is somewhat radially asymmetrical and its basal and 
stem end stands usually at an angle of about 45° from the 
horizontal as is shown in figure 10. The roots arise in a cres- 
cent shaped area whose center is at the lowest point. The 
bases of the leaves and scales are hollow cylinders and are 
attached on a slant that corresponds to the inclination of the 
nodes. If a plant is to remain vegetative for a season and 
is not to produce a flower, one of its leaves develops as a green 
aerial leaf and the scales outside of this together with their 
nodes die. The stem segment from which the green leaf arises 
increases in diameter and forms the base of the new bulb 
which thus becomes of greater width than the old stem seg- 
ments immediately below in which growth had ceased. But 
the radial growth of scales and stem segments of the new bulb 
is eccentric and is greatest toward the lower side. The new 
bulb, therefore, protrudes beyond and slightly below the part 
of the old stem of which it is an extension. This condition is 
readily revealed by a longitudinal section through a bulb (see 
fig. 10). The condition is shown diagrammatically in figures 
13, 16, and 17. In this ordinary growth of vegetative tulips, 
however, there is scarcely any elongation of the segments 
between the leaves (the internodes) and the entire stem is 
composed almost entirely of nodes to which the leaves are 
attached. 
The method of growth by which a bulb burrows to lower 
depths is a further development or modification of the proc- 
esses which give the new bulb its eccentrically expanded base. 
