THE GAMETOPHYTE OF PSILOTUM. 
91 
dividing walls (a), ( b ), (c). The apical cell (d) contains a few chromatophores from which the colour has, for 
the most part, diffused. 
Figs. 9-14. Prothallia of Psilotum in different stages of development, all drawn to the same scale. Figs. 
9-13 are perfect prothallia. The ends of the pro thallium in fig. 14 have been broken off. Most of the 
rhizoids have been removed from all the prothallia. In fig. 14 the antheridia are shown as small pro- 
tuberances, and patches of brown, dead superficial cells give the prothallium a speckled appearance. 
Fig. 15. Transverse section of a prothallium, showing the disposition of the endophytic fungus in dense 
skeins in the interior cells. 
Fig. 16. A rhizoid, showing two fungal hyphse entering it. One of them traverses the rhizoid to the 
extreme tip. 
Fig. 17. An internal cell of the prothallium, showing the passage of fungal hyphse through its walls. 
Fig. 18. A rhizoid, the end of which is broken off, leaving the fungal hypha within the rhizoid exposed. 
Fig. 19. The youngest part of a prothallium, showing the cells first formed after germination. They 
produce a cell-mass slightly different in character from the remainder of the prothallium. The dark line 
indicates the position at which the character of the cells becomes uniform, and beyond which the prothallium 
rapidly attains its maximum diameter. 
Fig. 20. Surface view of a pro thallium near the growing point, showing an archegonium as four rosette- 
shaped cells', and near to it wandering fungal hyphse are visible. 
Fig. 21. Surface view of a prothallium, showing several antheridia and three archegonia. Two of these 
are mature; they show the dark-coloured venter lying within the prothallium, bounded by four canal 
cells symmetrically arranged around the canal. The points at which numerous rhizoids have been broken 
off are seen as small circles in the centre of the cells. 
Fig. 22. A young archegonium from near the growing point. The four tiers of four canal cells are 
visible. 
Fig. 23. Section of an archegonium, showing the venter and the canal bounded by the four canal cells 
upon either side. 
Fig. 24. Section of an archegonium from which the upper three tiers of canal cells have broken off, the 
edges of the basal ones only being attached to those that remain. The oosphere, with a nucleus and nucleolus, 
is seen within the venter. Two deeply staining bodies, one in the nucleus and one in the cytoplasm, 
are present ; these are not always found. The venter has much-thickened walls ; so also have the basal 
canal cells. 
Fig. 25. The basal canal cells surrounding the canal seen obliquely upon the surface of the prothallium. 
Fig. 26. Section of a young antheridium, showing the spermatozoa! mother-cells. 
Fig. 27. View of a mature antheridium. 
Fig. 28. Four spermatozoids ; two show the spirally wound body. Upon one the numerous cilia are 
visible. 
Fig. 29. Surface view of a portion of the prothallium, showing three antheridia and a bulbil upon its 
stalk. Near the bulbil the neck of an archegonium is visible. 
Figs, 30 and 31. Stages in the development of a bulbil. 
TRANS. ROY. SOC. EDIN., YOL. LIT, PART I (NO. 3). 
14 
