of the Nuclei in Peronospora parasitica . 133 
fresh state, as highly refractive bodies, which may be vacuoles 
or accumulations of hyaline protoplasm. 
The observations which follow, upon the nuclei in the various 
organs of the fungus, have been made almost entirely upon 
sections obtained by means of the ribbon-section-cutting 
microtome, and stained with haematoxylin. 
The Nuclei of the Hyphae. 
The hyphae are much-branched tubes which ramify in all 
directions between the cells of the various tissues of the host 
plant. They contain a considerable quantity of protoplasm, 
which forms a thick parietal layer on the walls of the hyphae, 
enclosing a central cavity, across which numerous thick proto- 
plasmic strands pass. In certain places, however, the hyphae 
appear to be full of protoplasm, and it is probable that at 
these points rapid growth or elongation is taking place, 
Nuclei are found in large numbers in the protoplasm in all 
parts of the mycelium, both in the parietal layer and in the 
protoplasmic strands, but in those places, mentioned above, 
where the hyphae appear to be completely full of protoplasm, 
the number of nuclei present is considerably increased, and 
they form a not inconsiderable portion of the contents of the 
hyphae. In other places, however, the nuclei are comparatively 
few in number, and are scattered here and there, often at 
considerable intervals, in the protoplasm. 
The nuclei, in the resting stage, are spherical or slightly 
oval bodies. In those parts of the hyphae which appear to be 
rapidly growing the nuclei may become considerably elongated 
and deformed. Each nucleus is vesicular, and contains a con- 
siderable quantity of chromatin, which is arranged peripherally 
on its wall (Fig. 1, 1 ). In some nuclei the chromatin appears 
to form a continuous ring, while in others it is broken at one 
or more points, and in others again it presents a somewhat 
granular appearance. It is therefore probable that the chro- 
matin-body is of a somewhat irregular shape, and may form 
a coarse network of very thick threads ; or it may be divided 
