A STUDY OF PLASTIDS AND MITOCHONDRIA 
225 
sharply defined appearance and bright color, becoming gradually dimmer. 
Still farther back in the tip the red color disappears entirely, the plastids 
appearing more or less opaque or more uniformly blue in color, as shown in 
figure 6, g, h, and i. 
It has not been possible to determine, so far, how this association of the 
bright red granules with the light blue plastids comes about, though it might 
be imagined, from observations I have made, such as the appearance of 
two darkly staining red granules at the ends of a light blue ellipsoid, that 
the mitochondria are surrounded by, or become surrounded by, a substance 
which makes up the body of the plastid ; that they divide within this plastid 
substance and afterwards produce the starch grains within it, or themselves 
become changed into starch. This appearance suggests a relation to starch 
formation similar to that of the pyrenoid, as described by McAllister ('14). 
In other cases, however, bodies were observed which are made up of a 
dark red peripheral layer surrounding a light blue center. Both the latter 
structures and the ellipsoids occur in the intermediate regions of the peri- 
blem, between the red-staining mitochondria and the blue plastids with 
their red, granular inclusions. I wish to emphasize the fact that both the 
mitochondria and the plastids are exceedingly numerous in the regions 
indicated and that the staining reactions and the differentiation of the bodies 
described as occurring in the plastids are very definite. In many cells of 
the periblem, in the intermediate region of the tip, the nucleus is practically 
surrounded by a number of large plastids containing red-staining granules* 
while the cells nearer the tip are crowded with mitochondria which also 
color strongly with the safranin. Nevertheless, while the existence of 
these bodies is clearly demonstrable, I do not wish to imply that the seriation 
to prove their inter-relations is equally evident. 
Preissia commutata 
The situation in connection with the cytoplasmic inclusions of the 
liverworts and of the Bryophyta in general, appears to be in special need of 
investigation, not only on account of the fact that a perusal of the literature 
shows a considerable difference of opinion as to the real nature of the various 
bodies in question, but also on account of the very great interest attached to 
the group by virtue of its intermediate position in relation to the flowering 
plants on the one hand, and to the algae on the other. 
While the interest centers mainly in the plastids and their genetic 
relations, the oil bodies of the liverworts have received considerable atten- 
tion from investigators, with no very definite results as far as their real 
nature and origin is concerned. Pfeffer ('74) is credited with having made 
the first really fundamental and comprehensive study of the oil bodies. 
In his opinion they are formed by the aggregation of a large number of 
small oil droplets which are already visible in the very young cells. While 
he, at first, maintained that the bodies originate in the cell sap, he later 
