THE GAMETOPHYTE GENERATION OF THE PSILOTACEJE. 
Ill 
Fig. 16. This figure likewise represents a longitudinal section of a mature archegonium about the same 
stage as that shown in fig. 15. The upper tiers of the neck cells have broken away, hut traces of the cell 
walls of the second tier are to he seen. A dense cytoplasm and a large egg nucleus are conspicuous features 
of the venter. x 290. 
Fig. 17. The stage represented here is about the same as that in fig. 16. Only the lower -tier of 
neck cells is present, hut this tier (as shown in figs. 15 and 16 also) projects slightly over the surface of the 
prothallus in a very characteristic fashion, with thin curiously pointed margins. This archegonium is ready 
for fertilisation, x 290. 
Figs. 18-43 are of Psilotum triquetrum. 
Fig. 18. This is a representation of an entire prothallus of Psilotum. It is more or less cylindrical in 
form, branches irregularly, and with numerous long rhizoids growing out in all directions from the 
superficial cells. There is a merismatic organic apex at the end of each branch, and over the surface of the 
prothallus there are numerous antheridia and archegonia. The endophytic fungus inhabiting the cells of 
the prothallus is quite observable from the surface view, x 55. 
Fig. 19. This is a superficial view of an exceptionally large prothallus of Psilotum. The portion here 
represented is only half the length of the specimen, which was over half an inch long. The immense 
number of antheridia and archegonia projecting from its surface was very striking. These reproductive 
organs were just as numerous on the one side as on the other, and the prothallus itself was nearly perfectly 
cylindrical. The rhizoids and endophytic fungus are also very obvious. x 55. 
Fig. 20. This figure represents a transverse section of the prothallus of Psilotum. The main characters 
of the prothallial cells with their cytoplasm and nuclei are indicated. The distribution of the endophytic 
fungus is also shown. The hyphse of the latter are seen in only a few of the superficial cells, but quite 
conspicuous in the interior cells of the prothallus. x 75. 
Fig. 21. This is a representation of a longitudinal section through the merismatic apex of the prothallus. 
The apex consists of a mass of small cells with dense cytoplasm and deeply staining nuclei. One of these 
cells (marked Ap) I interpret to be the apical cell. It will be observed that none of the cells in this 
merismatic region are infected with the fungus, x 75. 
Fig. 22. We have here represented a longitudinal section of the prothallus taken some distance behind 
the apex. It shows the fairly even distribution of the endophytic fungus throughout the prothallial tissue, 
but the superficial cells are practically free from infection, only a few of the cells containing hyphse. x 75. 
Fig. 23. A transverse section through the prothallus. The presence of endophytic fungus is clearly 
indicated, and four mature antheridia are shown. One of the latter is empty, and the other three clearly 
show numerous coiled spermatozoids. x 75. 
Fig. 24. This figure represents an entire prothallus of Psilotum. It is comparatively of small size, but 
sufficiently old to. bear several antheridia and archegonia. The curious indefinite sort of branching is 
indicated, as well as the merismatic apices of the branches. The spherical form of the antheridia and the 
straight tube-like nature of the necks of the archegonia are clearly shown (Ar., An.), x 55. 
Fig. 25. This figure represents a few cells from the interior of the prothallus, as seen ip transverse 
section. It shows the effect of the endophytic fungus in the cytoplasm and nuclei of the prothallial cells. 
In the more advanced stages the nuclei have completely disintegrated, and the hyphse become coiled in dense 
masses, and fill the main space of the cell cavity. The phycomycetous nature of the fungus is also indicated 
in its non-septate hyphse. x 290. 
Fig. 26. We have here a representation of a transverse section of the prothallus. In the one plane 
three antheridia and four archegonia are shown. Two of the antheridia contain mature coiled spermatozoids, 
and the archegonia appear to be ready for fertilisation. The terminal tiers of the neck cells of the archegonia 
have broken away, and the egg cell is clearly visible in the venter. x 75. 
Fig. 27. This figure represents another section similar to that shown in fig. 26. There are two 
antheridia to be seen, one of which has discharged its spermatozoids. Two archegonia are to be seen, and 
these show the conspicuous egg cell in the venter and end cells of the neck broken away. The archegonia 
are ready for fertilisation. This and the preceding figure show the presence of the fungus in the interior of 
the prothallus. x 75. 
