THE GAMETOPHYTE OF PSILOTUM. 
87 
either near, the summit or base ; the latter, at its junction with the spore, exhibits a well-defined ring of brown 
cells, encircling an opening, leading from the interior of the spore into the hollow part of the dome. The 
projecting cells may represent the tips /of archegonia. Sections will be required to settle the question. 
Failing to secure ripe spores of Tmesipteris, old synangia were dissected. Traces of both male and female 
gametophytes were found, proving that the spores often germinate in capsules. After this discovery, further 
examinations of the old synangia of Psilotum were made. Many contained self -germinated spores, and 
afforded a better supply of material for study than by cultivation.” 
4. The Mature Prothallus. 
The mature prothallus is a cylindrical, single ox branched, saprophytic body, 
subterranean, light brown in colour, radially symmetrical, and densely covered with 
long brown rhizoids. It is monoecious. It is best obtained by taking a quantity of 
earth from fissures in rocks where Psilotum is growing, teasing up the earth finely 
and spreading it as a thin layer over the surface of a sheet of white paper, and 
examining the earth with a hand lens magnifying 15 diameters. 1 first discovered it 
in this way. 
Moist earth from deep in the rock fissures, scraped out with a steel wire with the 
end flattened and bent at right angles, must be examined. If fissures can be found 
below a spot where a clump of Psilotum plants have long ago established themselves 
so that the neighbourhood has become well dusted with ' spores, the locality is a 
hopeful one. Searching on the surface or on the ground-level is useless, and even in 
a favourable locality some bucketfuls of soil may be examined without success. 
The prothallia may be found in various stages of development from November 
till February. The branching of the prothallium is quite irregular, the most usual 
form being a short growth from the spore and then the formation of two branches of 
unequal length. The average diameter of a branch is from 468 /x to 655 /r, and the 
average length about 2457 p. 
The growing point is light yellow or white in colour, very obtuse, and differentia- 
tion behind it is very rapid. If a prothallium has received a check there may be a 
slight constriction behind the growing point. Normally the prothallium is turgid 
and brittle ; it soon becomes flaccid in the absence of moisture, but quickly regains 
its turgidity in water. Occasionally a prothallium may be found the distal end of 
which is dead, while the end near the growing point is alive and produces normal 
antheridia and archegonia. 
As the prothallus pushes its way through the rock crevices or gritty earth, some 
of the cells near the growing point are very liable to be injured, there being no 
root-cap. Such injured cells turn a dark brown colour, they frequently lose their 
nuclei, and later stand out in little groups of from three to eight cells as characteristic 
brown patches upon the surface of the prothallus. 
The general external cells are elongated, thin-walled, light brown in colour, and 
have conspicuous nuclei. 
Frequently ramifying over the surface of the prothallus, fine brown non-septate 
TRANS. ROY. SOC. ED1N., VOL. LII, PART I (NO. 3). 13 
