of Peronospora parasitica. 
279 
EXPLANATION OF FIGURES IN PLATE XVI. 
Illustrating Mr. Harold Wager’s paper on Peronospora parasitica. 
All the figures have been drawn with the aid of the camera lucida, and the 
apochromatic 2-0 m.m., 1*40 apert., of Zeiss, with ocular 8 (x 1000). The details 
were filled in with the aid of a magnification of 1500 (ocular 12), or 2250 
(ocular 18). 
Fig. 1. Young oogonium with antheridium and receptive papilla. 
Fig. 2. Nuclei in the periplasm in process of division. The antheridium has 
put out a fertilizing tube, and the central body is just beginning to form in the 
ooplasm. 
Fig. 3. Mitosis just completed; the central body is slightly more prominent. 
Fig. 4. The central body is now very distinct, and a single nucleus from the 
periplasm is in contact with it. A nucleus is just about to pass from the anther¬ 
idium into the fertilizing tube. 
Fig. 5. The cytoplasm of the oosphere is finely vacuolate. A nucleus is seen 
in the fertilizing tube. There is now a distinct line of demarcation between the 
ooplasm and periplasm. 
Fig. 6. A stage slightly later than Fig. 5, showing the first indication of the 
wall of the oosphere. 
Fig. 7. Fertilizing tube nearly in contact with the female nucleus. It appears 
as if about to open at the apex. Two nuclei are to be seen in it. 
Fig. 8. The sexual nuclei shortly after the entry of the male nucleus into the 
oosphere. The central body is already not so prominent and is beginning to 
disappear. 
Fig. 9. Later stage: the nuclei are at some distance from one another. The 
wall of the oosphere is now very prominent. 
Fig. 10. The sexual nuclei at a later stage. The apparent difference in size 
is due to the fact that one nucleus is seen from the end, the other from the side. 
Fig. 11. The sexual nuclei in close contact. They are just beginning to fuse. 
Fig. 12. The sexual nuclei in early stage of fusion. The cytoplasm contains 
large vacuoles. 
Fig. 13. Later stage of fusion. - 
Fig. 14. Nuclei completely fused to form a single oval nucleus. The nucleoli 
are still visible. 
Fig. 15. Fusion-nucleus, showing a distinct network and a single nucleolus. 
Fig. 16. Nearly ripe oospore with single nucleus. 
Fig. 17. Nearly ripe oospore with oogonial wall, showing how the periplasm is 
deposited on the wall of the oospore to form the exosporial layer. 
