59i 
Ford. — The Anatomy of P "silo turn triquetrum. 
leaves are bi-lobed, a feature which makes it easy to locate even very 
young sporangia. The sporangia themselves are for the most part tri- 
locular, but bilocular ones are occasionally found. 
The Rhizome. 
The much-branched rhizome of P silo turn bears no leaves or roots. 
In texture it is much softer than the aerial stem, and the surface is generally 
covered with fine, brown hairs, though these may be better developed 
in some regions than in others. The apices of the branches are white and 
naked, and the whole rhizome forms a somewhat confused mass of 
branches, which cannot be disentangled without breaking. Small circular, 
or oval, white spots occur at intervals on the branches ; these are destitute 
of hairs, and may be sunk or slightly raised above the surface. They 
represent dormant lateral buds which are capable of resuming growth 
under favourable conditions. 
Here and there some of the rhizome-branches assume a vertical, instead 
of a horizontal, position, and grow upwards towards the surface of the soil ; 
these are future aerial branches. As they develop, the superficial hairs 
disappear and the surface becomes smooth and hard, and small scale-like 
leaves shortly make their appearance. 
Before passing to the internal anatomy, reference must be made 
to Professor Bertrand’s 1 detailed account of Psilotum. In regard to 
the external structure, Professor Bertrand has described the aerial stem 
under the heads of ‘ cladodes “ souches,” ’ ‘ cladodes of the first, second, 
third, &c. order,’ ‘ terminal and sporangiferous cladodes,’ and ‘ simple, 
aerial branches/ the last being only occasionally found. Similarly, the 
underground portion has been subdivided into ‘ simple subterranean 
branches ’ and c sympodia ’ of these, and ‘ subterranean cladodes ’ and 
‘ sympodia of cladodes 2 .’ These structures have not the same morpho- 
logical value. The ‘simple branches’ are to be considered as such, whilst 
the ‘ cladodes ’ and ‘ sympodia of cladodes ’ are to be regarded as consisting 
of two or more stems which are united throughout the greater part of their 
course. At the apex, however, their real nature may be detected, this 
being shown by the presence of two or more ‘ centres of growth ’ being 
always found, each of which may possess a distinct apical cell. The 
first elements of the xylem-strand to be differentiated below the apex 
consist of two or more separate groups of spiral tracheids, each group 
corresponding to an apical ‘ centre of growth,.’ 
1 Bertrand (’ 81 ), p. 252, et seq. 
2 It is of course open to question whether the term c cladode ’ can rightly be used in regard to the 
rhizome ; cf. Goebel’s definition of the term, viz. ‘ a branch consisting of one internode counterfeiting 
a leaf.’ The branches of the rhizome of Psilotum are brown, and destitute of chlorophyll ; they 
fulfil the functions of roots, and have not the slightest resemblance to leaves. 
