THE GAMETOPHYTE OF PSILOTUM. 
81 
While Psilotum appears to be usually confined to the situations above described, 
and Tmesipteris is generally to be found upon tree ferns or upon Todea, nevertheless 
I have found Tmesipteris growing side by side with Psilotum in rock crevices, and I 
have found Psilotum growing upon Todea ; a fact which suggests that the endophytic 
fungus found in Psilotum and in Tmesipteris is the same species, and that, while one 
plant is mainly xerophytic in character and the other hydrophytic, variations in the 
aerial structures may occur according to the environment, as is indeed the case. 
Psilotum varies very considerably according to the situation in which it occurs. 
In exposed situations the aerial parts tend to become short and stocky ; in sheltered 
situations they tend to become flaccid and pendulous, while the prominence of the 
ridges is diminished. 
The rhizome will travel several feet in rock fissures, throwing out aerial branches 
at favourable situations. 
Openings in the exposed surface of a rock, apparently quite separate, are frequently 
united further in as one continuous fissure, and at such openings the aerial parts of 
Psilotum make their appearance. 
The sporophylls of Psilotum start to produce ripe synangia at the beginning of 
September, and further sporophylls develop and produce spores till the end of March. 
At about this time the first shoots of the sporophylls and foliar organs for the ensu- 
ing year make their appearance, and have pushed well forward by the end of April. 
Belated sporophylls that have failed to mature their spores in March may last on 
through the winter ; those whose spores have been shed wither and die. 
The sporophylls from very young rhizomes are simple and unbranched, or they 
consist of a single fork ; as the rhizome ages the dichotomous branching becomes 
more and more extensive. 
The synangia are at first covered with a green coat ; as they approach maturity the 
green colour is rapidly changed to a brilliant yellow. A day or two later the yellow 
colour changes to light brown, the dividing septa split, and the three chambers of the 
synangia open. The spores are disseminated by the wind. After their discharge the 
chambers almost close and the synangium turns a dirty brown and frequently drops off. 
In this condition it often contains a residue - of undischarged spores. These 
synangia are sometimes collected by ants and carried into clefts in the rocks. In 
this way some spores of Psilotum may be sown in surroundings congenial for their 
germination ; for the rest, it is a fortuitous circumstance if they happen to be blown 
by the wind into a suitable situation. The following case illustrates how necessary 
it is to have every condition satisfied. In the Hawkesbury River is a rocky island 
about eighty' acres in extent, distant about half a mile from the mainland. Upon 
this island I lived for three months : I had, therefore, every opportunity of becoming 
familiar with the flora. One solitary specimen of Psilotum was found which, judg- 
ing from its size, had produced spores for years, yet no indication of any other 
Psilotum plant was ever found upon the island. 
