97 
of Chloroplasts and Leucoplasts. 
numerous. Some of the granules present a smoother contour than others. 
The rods vary in length, and to some extent in thickness. Some are club- 
shaped and some dumb-bell-shaped. In cells of the root-cap the rounded 
granules far exceed the rods in number as in Pisnm. In the older parts of 
the root-cap, where the cells have begun to round off and separate from 
each other, rounded leucoplasts with their starch inclusions are present and 
confined chiefly to the distal ends of the cells, although a few are dis¬ 
tributed throughout the cell. The transition of the short rod-shaped 
primordia, through club-shaped, pear-shaped, and hand-mirror-like forms, so 
conspicuous in Pisum , is not so easily observed in the root-cap of Zea. 
Some of the leucoplasts arise from rounded primordia, these appearing at 
first only slightly larger than the densely-staining granules, but with 
a sharp contour or rim and a colourless, or only slightly stained, centre. 
In Zea such very small leucoplasts are present in small numbers in the 
meristematic cells. In cells of the dermatogen and plerome, the trans¬ 
formation of rod-shaped primordia through the forms just mentioned is 
conspicuous. As in Pisum , there are also present, in addition to the 
primordia, the very numerous rounded chondriosomes. They persist 
in large numbers even in older cells. The behaviour and fate of both 
plastids and chondriosomes is the same as that described for Pisum. 
Marchantia . No other plant selected by me for study shows more 
clearly the sharp and well-defined difference between chloroplasts and 
the rod-shaped or granular bodies which are not chloroplasts and which do 
not develop into chloroplasts, but which reveal and retain their identity in 
both young and old cells. 
In Fig. 5 we have a longitudinal vertical section through the growing 
point of the thallus, including one apical cell and two young ventral scales. 
In the apical cell, and in those touching it, are to be seen the young rounded 
chloroplasts and the very small rod-shaped and granular bodies. The 
groundwork of the cytoplasm is illustrated by fine stippling. In older 
cells, removed two or three layers from the apical cell, the difference 
between the rounded chloroplasts and the rod-shaped chondriosomes is 
more obvious. Fig. 6 is a cell taken a little farther back from the growing 
point than those in Fig. 5. Here some of the chloroplasts appear more 
rounded and larger, probably with a flat side turned towards the observer. 
Others are narrower and lenticular in shape with a light strip running length¬ 
wise through the middle. In this position the chloroplasts present a view 
not unlike the flattened side of a grain of wheat or a coffee bean (see also 
Fig. 6). The chloroplast in these cells seems, therefore, to be a flattened 
object, round, oval, or elliptical when viewed from the flat side, but somewhat 
lenticular when seen from the edge. In older parts of the thallus, the 
colourless, lenticular centre is, doubtless, an inclusion of starch. In some 
instances the chloroplasts in older cells present the appearance of Fig. 14 ,a y 
H 
