260 Campbell. — On the development 
once by means of segments cut off from it in the same way as 
the primary root. The first trace of the vascular bundle is 
formed at a point in immediate contact with that of the leaf 
(Plate XV, Fig. 7), and its development proceeds from this 
point toward the apex of the young root. 
The apex of the stem grows slowly, producing from time to 
time a complete set of segments in rapid succession, and then 
resting for some time before another set is formed, so that 
there is always considerable difference in the ages of any two 
succeeding sets of segments ; and as the segments divide 
rapidly after being formed, if the apex of an older plant is 
examined (PI. XV, Fig. 9), while the youngest set of segments 
may be perfectly plain, it is not easy to trace the limits of the 
older ones. From the slowness with which new segments are 
formed, and the crowded manner in which the young leaves are 
arranged, it is probable that each segment gives rise to a leaf, 
or rather that the two dorsal segments of each set form 
leaves, while the third, or ventral segment, gives rise to a root, 
at least the regular occurrence of roots in relatively the same 
position to the apical cell of the stem, as the young leaves 
would indicate that this is the case (PL XV, Fig. 9 r). All the 
roots however cannot be thus formed, as their number exceeds 
that of the leaves, and it is highly probable that the others 
originate from the bases of the leaves in the same way as 
the second root. 
Owing to the rapid growth of the young leaves, and the 
slowness of that of the apex of the stem, the latter becomes 
more and more sunk, until after three or four leaves are com- 
pletely grown it scarcely projects at all. The younger por- 
tions of the stem and leaves are more or less covered with 
short-jointed hairs, which also covered the growing-point of 
the stem to a certain extent. The elongation of the stem 
is due almost entirely to intercalary growth of the older 
segments. 
The first leaves show scarcely a trace of the coiling that 
characterizes the young leaves formed later, but this becomes 
more and more evident as the plant grows. 
