3 1 6 
Lang . — The Prothallus 
EXPLANATION OF FIGURES IN PLATES 
XVI AND XVII. 
Illustrating Mr. W. H. Lang’s paper on The Prothallus of 
Lycopodium clavatum , L. 
PLATE XVI. 
Fig. i. Photograph of a prothallus of Lycopodium clavahtm and of a young 
plant free from the prothallus. Natural size. 
Fig. 2. The smallest prothallus found, seen from above, x 7. 
Fig. 3. Prothallus bearing numerous antheridia on ridges just within the lateral 
margins : a from the side, b from above, x 7. 
Fig. 4. The largest prothallus found, seen from the side. The two ends are in 
contact, x 7. 
Fig. 5. Part of a transverse section of the prothallus in Fig. 3 including the 
margin : a-f, the layers of tissue described in the text ; x position of the marginal 
meristem. The shaded cells are those within which the endophytic Fungus was 
present, x 80. 
Fig. 6. Lower portion of a similar section of the same prothallus including 
cells of the layers «, b, c, and d. x 375. 
Fig. 7 a, b. Median sections through the ends of a prothallus to show the 
difference of outline that may exist between them, and for comparison with sections 
across the lateral margin : x position of meristem. x 25. In this and in the 
other outline figures of sections through the prothallus (Figs. 8, 9, 25 and 26) the 
darker shading indicates the region in which the mycorhizal Fungus is intracellular, 
the lighter shading the layer in which it is intercellular. 
Fig. 8. Vertical section across the margin of the prothallus in Fig. 4 to show the 
marginal ridge and succession of archegonia. x 35. 
Fig. 9. Similar section of the prothallus in Fig. 3 showing the succession of 
antheridia on the marginal ridge, x 35. 
Figs. 10-12. Stages in the development of antheridium ; the cells which give 
rise to the spermatozoids are shaded, x 530. 
Fig. 13. Longitudinal section of an almost mature antheridium. x 375. 
Fig. 14. Transverse section of an almost mature antheridium. x 375. 
Figs. 15, 16. Arrangement of cells forming the free part of the antheridium- wall. 
The triangular cell in the centre has broken down to allow of the escape of the 
spermatozoids. x 375 - 
PLATE XVII. 
Figs. 17-19- Stages in the development of archegonium. x 375. 
Fig. 20. Longitudinal section of a mature archegonium. x 3 75. 
Fig. 21. Similar section of a mature archegonium in the development of which 
the divisions in the generative layer forming the ‘ false neck ’ are seen to extend 
to adjoining cells on the right-hand side of the figure, x 375. 
