88 
G. P. DARNELL-SMITH ON 
fungal hyphse are to be observed. In all cases in which I have grown Psilotum 
spores these brown thick-walled fungal hyphse have been present in the soil. 
The prothallus frequently has upon it small bulbils. Each is carried upon a 
short stalk with a transverse wall, and is very easily detached. In the young stage 
they are white and consist of four to six cells, with distinct nuclei surrounded by 
highly refringent granules. Later the cells of the bulbil become more numerous and 
darker in colour (figs. 29, 30, and 3l). 
Note. 
The prothallus described by Dr Lang * and provisionally referred to Psilotum would appear to have 
been that of some Lyeopod. 
5. Details of Vegetative Characters of the Prothallus. 
The details of the structure of the mature prothallus have been determined by 
the examination of a number of sections. 
In transverse section the prothallus is found to be nearly circular, and to consist 
of a number of thin-walled roughly pentagonal cells, bounded on the outside by 
oblong cells, slightly cuticularised externally. Many of these latter give rise upon 
slightly raised cushions to long brown tubular rhizoids. 
The whole of the cells of the prothallus may contain an endophytic fungus, but 
where it occurs there is no difference in the conformation or structure of the cells. 
Nearly all of the older cells except those of the external layer are usually filled with 
dense skeins of this endophytic fungus (fig. 15). It passes quite easily through the 
cell walls, and a pentagonal cell may frequently be observed with a dense fungal 
skein, obliterating the- nucleus, from which fungal hypha pass out through each of 
the five walls of the cell (fig. 17). In longitudinal section fungal skeins may be 
found in cells a short distance behind the growing point, and from these fungal 
hyphse extend as fine infection threads to the young cells. Fungal hyphen pass 
down the centres of many of the tubular rhizoids, their ends being in contact with 
the extreme tip of the rhizoid. Sometimes two hyphse occur in one rhizoid. The 
cell from which the rhizoid arises may have a fungal skein within it ; more usually 
the fungal hypha arises from a fungal skein contained in the cell immediately 
internal to that giving rise to the rhizoid (figs. 16 and 18). 
The thickness of the hyphse, which are non-septate and colourless, varies greatly. 
Fungal hyphse have been observed in the antheridia and in the canal cells of the 
archegonium, but not in the egg cell or in the chamber in which the egg cell lies. 
6. The Antheridium. 
The antheridia project freely from the surface of the prothallus. The antheridium 
encloses a large spherical mass of sperm-mother-cells which form spermatozoids 
* W. H. Lang, “ On a Prothallus provisionally referred to Psilotum Annals of Botany, vol. xviii, p. 571. 
