of the Nuclei in Peronospora parasitica. 145 
EXPLANATION OF FIGURES IN PLATE VI. 
Illustrating Mr. Harold W. T. Wager’s paper on the Structure of the nuclei in 
Peronospora parasitica. 
Fig. 1. Nuclei of the mycelium in various stages of division, x 1500 l . 
Fig. 2. Nuclei of the oogonium in various stages of division, x 1500. 
The numbers in the above figures denote the successive stages of division. 
Fig. 3. A small piece of the mycelium, showing nuclei at the time when the 
mass of chromatin is beginning to break up. x 1000. 
Fig. 4. Section of an oogonium just forming as an expansion at the end of a 
hypha. Numerous nuclei, n, in the resting stage have just passed into it from the 
mycelium, a, antheridium. x 1000. 
Fig. 5. Section of an oogonium and antheridium which have just been delimited 
from the thallus. The nuclei are slightly enlarged, and the chromatin is some- 
what broken up. x 1000. 
Fig. 6. Section of an oogonium at a little later stage than Fig. 5 ; the nuclei 
are larger and the thread structure is distinctly visible. Numerous vacuoles, v } 
are present, x 1000. 
Fig. 7. Section of an oogonium with its antheridium at the time when the nuclei 
are passing to the periphery of the oogonium, x 1000. 
Fig. 8. Section of an oogonium with its antheridium. The nuclei are arranged 
very regularly in the periphery of the oogonium. The central portion of the 
oogonium contains a quantity of less dense protoplasm, a, antheridium. /, peri- 
plasm. 0, protoplasm of the oosphere. x 1000. 
Fig. 9. Section through the peripheral portion of an oogonium at the stage 
shown in Fig. 8 so as to include a complete layer of the nuclei. The nuclei 
exhibit a thread structure, many of them in the stage just previous to division. 
Some very faint conical, slightly-stained masses, s, probably of the nature of a 
nuclear spindle, are to be seen in connection with many of them, n, nucleus seen 
from the end. n\ nucleus seen slightly oblique, x 1 500. 
Fig. 10. Section of an oogonium in which the peripheral nuclei have begun to 
divide. Three of the small nuclei, n , can be seen passing towards the centre of 
the oogonium, where they probably fuse together, x 1000. 
Fig. 11. Section of an oogonium in which the peripheral nuclei have divided up 
into a number of smaller nuclei, //. The wall of the oosphere, o, is just beginning 
to form, and appears as a somewhat granular layer, just inside the layer of peri- 
plasm, p . The nuclei of the antheridium, a, have also divided up in the same 
manner, a', antheridial tube. A single nucleus, n, is seen in the protoplasm of 
the oosphere. 
1 Except where otherwise stated the figures have been drawn by means of the 
camera lucida and the apochromatic object-glasses of Zeiss. 
L 
