Lang . — On a Prothallus provisionally referred to P silo turn. 577 
prothallus is really that of P silo turn . It will be of interest to see whether 
this assumption proves correct or not. In the meantime it would be obviously 
inadvisable to discuss the bearing of the type of prothallus on the question 
of the affinity of the Psilotaceae, further than to say that if this prothallus is 
proved to belong to P silo turn , it will lend support to the close association 
of the latter with the homosporous Lycopodiaceae. 
EXPLANATION OF FIGURES IN PLATE XXXVII. 
Illustrating Dr. Lang’s paper on a Prothallus provisionally referred to Psilotum. 
Fig. 1. The prothallus seen from the side, x 7. 
Fig. 2. The prothallus seen from the side and from above, x 7. 
Fig. 3. The prothallus halved in a plane parallel to but just avoiding the conical projection and 
viewed from the cut surface, x 7. 
Fig. 4. Section through the junction of the vegetative and sexual regions, showing the pro- 
tuberant edge of tissue bearing the antheridia ; the cross indicates the position of the meristematic 
region. x 25. 
Figs. 5, 6. Vertical sections through antheridia. x 375. 
Fig. 7. Vertical section through the mycorhizal region, showing the arrangement of the layers of 
cells inhabited by the fungus, a. superficial layer, b. layers with intracellular hyphae, c. layer 
of elongated cells with intercellular hyphae and vesicles, d. parenchymatous tissue free from fungal 
hyphae. x 200. 
Fig. 8. Diagrammatic section through the base of the prothallus and the primary tubercle, 
showing the distribution of the fungus, a. b.c.d ., as in Fig. 7. x 25. 
Fig. 9. Three of the multinucleate vesicles borne on the endophytic fungus, x 375 * 
