of Chlor op lasts and Leucop lasts. 103 
are of the same size and structure as in the apical cell. In the cells 
resulting from the second or third older segments, the primordia, now 
larger and more numerous, stain very densely. In slightly older cells some 
become club- and dumb-bell-shaped. In cells of the central cylinder, a little 
farther back, the densely staining rods are the most strikingly conspicuous 
objects in the cell. This is well illustrated in Fig. 15. Here it is seen that 
the rods vary in length, many being variously curved or bent. In addition 
to the rods, which are unquestionably derived from the primordia of plastids 
seen in the apical cell, there are the ever-present granules in countless 
numbers. They occur singly, in pairs, as if in division, and in chains. These 
granules do not constitute the groundwork of the cytoplasm (Fig. 15). In 
the narrow elements of the central cylinder of the root, which have dense 
cytoplasm, the rods are numerous and especially conspicuous, because they 
are thicker and stain densely. Many seem to be undergoing transverse 
division, but whether they break up into the small granules cannot be stated 
with certainty. The leucoplasts in the form of a hand-mirror, which are 
rather conspicuous in Pisum , are very rare in the fern and of a much 
smaller size. 
In the wider elongating cells of the central cylinder, which have sparse 
cytoplasm, the rod-shaped primordia of leucoplasts that fail to develop 
inclusions become greatly elongated and flattened threads staining a pale 
blue (Figs. 16, 17). They are undergoing disorganization, for in older cells 
they disappear. Figs. 16 and 17 represent tangential views of portions of 
two large cells of the central cylinder. In addition to the long and 
disorganizing threads are the very numerous small rods and granules, 
the chondriosomes, which are present in younger parts of the root and which 
do not seem to be derived from the plastids nor from the conspicuous rods 
that develop from the plastids. In Fig. 17, at the left, is seen a cluster of 
starch grains which, together with surrounding cytoplasmic granules, stain 
a pale orange. The group is the same as those described in a preceding 
paragraph for cells of the root-cap. 
The plastid primordia in the younger cells of the periblem and derma- 
togen are identical with those of the central cylinder, hut in this region, as 
the cells begin to elongate and enlarge, the primordia do not become long 
rods. These cells present a striking contrast, therefore, to those of the 
central cylinder with their numerous densely stained rods. In these periblem 
cells some of the primordia develop into rounded leucoplasts with starch 
inclusions ; others remain as they appeared in the younger cells. The small, 
densely-staining round chondriosomes, conspicuous as black or blue dots, 
are present in large numbers in both old and young cells of the periblem as 
elsewhere. In older cells of this region there remain in the cytoplasm the 
yellowish-staining clusters of starch grains, a few isolated leucoplasts, pale 
in colour, and the numerous round chondriosomes. 
