386 BOTANICAL GAZETTE [NOVEMBER 
Later stages of development 
The young frond now has present all the structural units which 
will be visible in the mature free frond, the later developments 
being in the manner of enlargement of parts present and the com- 
pletion of structures already initiated. The two buds in their 
respective pouches will follow the same stages as the frond develop- 
ing from an axillary bud, such as is being discussed; while the root 
shows little of special interest. Two changes which take place, 
however, should be mentioned; the rapid elongation of the region 
anterior to-the bud-root region, and the thrusting forward of the 
whole structure by the development of the basal region into a stalk 
or stipe. In Lemna this basal region is attached marginally to 
the main portion of the frond, but in Spirodela it is inserted upon 
the ventral surface some distance from the edge, and in Wolffa 
it is almost completely lacking. 
The axillary bud which was at first upon the dorsal surface of 
the stipe is forced into a-lateral position, as was the case with the 
frond bud which was divided. In this case the lateral shifting 
seems to be due to the more rapid growth of the stipe to one side of 
the median line, resulting in a tipping of the bud and raising its 
base as the stipe thickens. In the frond this stage is accompanied 
by the development of air cavities in the anterior region which is 
elongating rapidly. The individual cells become highly vacuo- 
lated, and the stomata are differentiated. The vascular strands 
appear at this time in the anterior region, which in all essentials 
assumes the structural characteristics of a foliage leaf. 
The vascular cells in the stipe become more clearly defined as 
a single strand centrally located in the tissues of the connecting 
structure. This strand ends in a confused group of cells at the 
point of origin of the vascular tissues of the root, the lateral buds, 
and the anterior region. This region corresponds to the mat of 
vascular elements in the base of a bulb as discussed by CHRYSLER’, 
and may be considered as locating closely the stem apex of the 
plant. In bulbs the apical region usually gives rise to a single main 
bud, with some lateral buds axillary to bud scales. In Lemna the 
4 Curyster, M. A., Development of the central cylinder in Araceae and Liliaceae. 
Bor. Gaz. 38:161-184. 1904. 
