Perithecium of Poly stigma mbrum, DC. 767 
EXPLANATION OF PLATES LXX AND LXXI. 
Illustrating the paper by Professor V. H. Blackman and Miss Welsford on Polystigma rubruin. 
PLATE LXX. 
The preparations are mostly from material fixed in Flemming’s strong fluid (half strength) or 
acetic alcohol and stained with iron-alum-haematoxylin. 
Fig. 1. Leaf-cells of host with hyphae of fungus pushing between them ; the cell on the right is 
dead and has darkly staining contents, x 1,200. 
Fig. 2. Later stage in the formation of a sclerotial patch. The host cells, with deeply staining 
tannin-like contents, are dead, and have been pushed apart by the action of the fungus, x 1,200. 
Fig. 3. Older hyphae of sclerotial patch with thick walls, showing fine pits, x 1,800. 
Fig. 4. Aggregation of hyphae beneath the stomata on the under surface of the leaf, x 900. 
Fig. 5. Section through leaf in the plane of the guard cells, showing one guard cell and hyphae 
projecting through the stomatal pore. X 800. 
Fig. 6. Section through leaf, showing a spermogonium. x 300. 
Figs. 7 a and 7 b. Two spermatia unstained and mounted in a watery medium. X 1,800. 
Figs. 8 a and 8 b. Stained spermatia, showing the elongated nucleus, x 1,800. 
Fig. 8 c. Spermatial hypha with base of spermatium above, with elongated nucleus. x J,8oo* 
Fig. 9. Very early stage in the development of an ascogonium ; the terminal portion of a vege- 
tative hypha shows four nuclei and is the future ascogonium. x 1 ,800. 
Fig. 10. Later stage in the development of the ascogonium, which has now become coiled, and 
shows at least one septum, x 1,800. 
Fig. 11. Section showing coiled ascogonium in the neighbourhood of a stoma through which 
ordinary vegetative hyphae are seen projecting. The four irregular masses are disorganized mesophyll 
cells, x 900. 
Fig. 12. Mature ascogonium of simple form, showing details of cells and nuclei. The basal 
end can be traced into a vegetative hypha, while the other ends freely. Some of the nuclei show 
a large nucleolus and little chromatin ; others show a small nucleolus and ample chromatin, 
x 1,300. 
Fig. 13. A more complicated ascogonium than that of Fig. 12. x 800. 
PLATE LXXI. 
Fig. 14. Abnormally branched ascogonium. One or more of the branches apparently projects 
from the stoma as an ordinary vegetative hypha. x 800. 
Fig. 15. Basal cell of ascogonium, showing a large number of small nuclei, x 1,200. 
Figs. 1 6 a and 1 6 b. Several cells of an ascogonium, showing the distinction of size and appearance 
of the nuclei, x 1,200. 
Fig. 17. Early stage of perithecium as a cone-shaped mass of vegetative hyphae. The dis- 
organizing ascogonial cells are seen at the periphery and at the centre, x 800. 
Fig. 18. Young perithecium a little older than that of P'ig. 17. The ascogenous hyphae are not 
yet clearly to be distinguished, but many of the nuclei of the perithecial cells are clearly arranged in 
pairs. The darkly stained masses at the periphery are the disorganizing cells of the ascogonium. 
x 800. 
Fig. 19. Later stage of young perithecium with ascogenous hyphae well differentiated by their 
larger size, denser contents, and larger nuclei. Remains of ascogonium still visible, x 1,200. 
Fig. 20. Section through base of young perithecium at a time when the ascogenous hyphae are 
becoming differentiated. There are indications of nuclear fusions, especially at the point marked 
with a star, and also in the paired condition of many nuclei and the larger size of others, x 1,800. 
Fig. 21. Cells at base of young perithecium with two nuclei in contact, indicating a stage before 
fusion, x 1,800. 
Fig. 22. Young ascus still binucleate, occupying the typical position at end of an ascogenous 
hypha. x 2,700. 
Fig. 23. An ascus in a stage somewhat later than that of Fig. 22. The two nuclei have fused, 
but the nucleoli remain distinct, x 1,800. 
Fig. 24. Section through mature perithecium. Many of the younger .asci are disorganized, 
x 300. 
