Watson on Structure and Relation of the Plastid. 341 
coarsely alveolar nature, within is a very densely staining 
nucleolus. A number of the plastids are observed to con- 
tain a single body, each of the same general size, density 
and staining quality as the nucleolus. Indeed, without other 
evidence, this is the only fact that would cause suspicion of 
relationship between the nucleus and the plastids. 
The plastids divide by fission as is shown in Fig. XII 
(d), where the constriction is just beginning. 
Funaria hygrometrica.—The thin new leaflets stained in 
eosin and mounted in balsam were used. The large rather 
flattened cells near the margin of the young leaves toward 
the tip were most favorable for study. 
The plastids are large and stain deeply, they are made up 
of a granular or alveolar structure quite similar to the 
nucleus. 
The multiplication is by simple fission, and in cells in this 
position it will be seen by Fig. VII that divisions go on very 
rapidly. 
It will also be seen that the plastids are joined together 
by fibres, and that in some cases, for example, Fig. VII (s), 
a definite system has been formed, t. e., we can easily under- 
stand how a group of plastids might arise from one parent 
through successive divisions, and that these might ai! remain 
joined by filaments which persist as the attenuated connect- 
ing strand formed when two plastids drew apart. 
Prothallus of Fern (Adiantum ).—The plastids are packed 
quite closely. The nuclei are but little larger than the plas- 
tids. In structure, both plastid and nucleus are identical, 
though the nucleus probably stains slightly the deeper. 
The connecting fibres show no definite system, owing to 
the great number of divisions that take place. They divide 
by amitosis as in Fig. XVIII (a), (b), (c). 
Fig. XIII shows a peculiar type of plastid occurring in the 
subepidermal tissue of Pteris bicolor. A limited number of 
these occur in the different cells. They closely simulate 
nuclear characters, bands of substance winding in a merid- 
