620 Pearson. — The Micro sporangium and Microspore of Gnetum. 
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p. i. 
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Buit. [2], vol. i, p. 46. 
(’03) : Parthenogenesis bei Gnetum U/a, Brongn. Flora, Bd. xcii, p. 397. 
Pearson, H. H. W. (’06) : Some Observations on Welwitschia mirabilis , Hook. f. Phil. Trans., 
B., vol. cxcviii, p. 265. 
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(’80) : Zellbildung und Zelltheilung. Ed. 3, Jena, 1880. 
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Welwitsch, F. (71) : Sertum Angolense. Trans. Linn. Soc., vol. xxvii, p. 1. 
EXPLANATION OF PLATES LX AND LXI. 
Illustrating Prof. Pearson’s paper on the Microsporangium and Microspore of Gnetum. 
Figs. 5-20 — G. africanum. 
Fig. T. Male spikes of Gnetum . a, G. scandens ; b, G. africanum', c, d, G. Buchholzianum. 
(a, b, c = natural size ; nf=enlarged). 
Fig. 2. Tangential longitudinal section through a node of the male spike of G. africanum . 
The stages of development shown by the anthers are as follows : 
1,1', 2 = free microspores (uninucleate). 
3' = microspores almost free of mother-cell wall. 
3 =. ,, enclosed in mother-cell wall. 
4 = spireme condition of mother-cell nuclei. 
4' = synapsis „ „ ,, 
5, 5', 6 = sporogenous cells earlier than mother-cell condition, x 28. 
Fig. 3. Transverse section of the axis of the male flower of G. africanum above the insertion of 
the perianth, showing the two xylem strands, x 305. 
Fig. 4. An exceptional type of hair inserted on the axis of the inflorescence among the male 
flowers (G. Buchholzianum'). x 305. 
Fig. 5. Transverse section through part of a young anther, x 600. 
Fig. 6. A later stage showing the enlargement of the cells of the inner tapetum and the ex- 
haustion of those of the outer, x 600. 
Fig. 7. Section through part of the anther wall passing through line of dehiscence, x 305. 
Fig. 8. Spore mother-cells a little before the ‘synapsis’ condition. The cell-walls at this stage 
are very delicate and with difficulty to be distinguished, x 940. 
Fig. 9. Spore mother-cells at a later stage. The wall is everywhere distinct and much 
thickened in places. The separation of the cells is nearly complete. One of the two cells of the 
inner tapetum is binucleate. x 1,000. 
Fig. 10. Spore mother-cells before the commencement of the homotypic division, showing 
a stage in the separation of the cells, x 1,000. 
Figs. 11 and 12. Spore mother-cells with their nuclei in course of the homotypic division, 
x 1,000. 
Figs. 13, 14 and 15. Stages in the septation of the mother-cell, x 1,000. 
Fig. 16. A mature microspore. x 1,000. 
Fig. 17. Germination of the microspore ; first mitosis, x 1,000. 
Fig. 18. Germination of the microspore ; binucleate stage, x 1,000. 
Fig. 19. Germination of the microspore; second mitosis, x 1,000. 
Fig. 20. Pollen-grain, x 1,000. 
