382 THIRD GROUP. VASCULAR CRYPTOGAMS. 



B. THE PSILOTACEAE 1 . 



The family of the Psilotaceae contains two genera, Psilotum and Tmesipteris^ 

 small shrubs with straggling branches, of which Tmesipteris belongs to Australia, 

 Psilotum to Madagascar, the Moluccas and the Sandwich islands. The slender stem 

 of Psilotum with its numerous long thin branches, which are all dichotomously 

 developed, rises above the ground in the form of a straggling shrub, and as it has no 

 roots, supplies their place with a system of branches from the stem ; the leaves are 

 few and developed only as small acute scales even on the aerial parts of the plant. 

 The sporangia appear three or four together on quite short and small lateral shoots 

 from the long branches, and do not form compact spikes. 



The stem of Psilolum is slender and many-angled, and bifurcates repeatedly ; its 

 subterranean shoots possess a three-sided apical cell, which according to Nageli and 

 Leitgeb forms three rows of segments ; these are spirally disposed on account of the 

 advance of the primary walls in the anodic direction, as in many Mosses. The leaves, 

 which are small and distant from one another and are even destitute of a vascular 

 bundle, show in their position on the angles of the stem no direct connection with its 

 die 1 otomies ; Psilot m tri l uelrum is entirely without roots, but produces a number of 

 underground shoots which fulfil the duties of roots and are extremely like them in 

 appearance. The shoots from the rhizome which approach nearer to the surface of 

 the ground have very minute subulate whitish leaves which may be seen with the aid 

 of a lens ; the shoots which lie deeper and are like roots are blunter at the extremity 

 and show no sign of a leaf even under the lens ; the anatomical structure of the former 

 is the same as in the true stems of the plant ; but in the latter the vascular bundles are 

 collected into an axile group, as in true roots. The shoots in which the rudiments of 

 leaves can be discerned can turn upwards, become green and develope into ordinary 

 foliage-shoots ; the root-like shoots, which are naturally more slender, may also turn 

 upwards and become thicker and assume the appearance of ordinary superficial 

 rhizome-shoots. In this respect therefore they differ at once from true roots, and still 

 more in the absence of a root-cap ; they terminate in an apical cell which forms 

 oblique segments inclining alternately in different directions. But the most important 

 point is that these shoots actually have rudiments of leaves which consist of a few cells, 

 and do not burst forth above the surface but remain concealed in the tissue. They 

 are most easily recognised in a longitudinal section, and may be seen to consist of an 

 apical cell and from two to five cells with the arrangement characteristic of leaves. 

 Similar few-celled rudiments of leaves occur also on ordinary rhizome-shoots, but 

 there they develope further, especially if the extremity of the shoot comes above the 

 ground. The root-like shoots branch in the same way as the ordinary shoots. 



Whether Tmesipteris has similar underground shoots, or true roots, appears not 

 to be known; the plant has not been studied in the living state, and herbarium 

 specimens which I have seen show only portions of the shoots. The leaves which 

 appear to grow erect are considerably larger than in Psilotum and are traversed by 



1 [Solms, Der Aufbau d. Stockes v. Psilotum triquetrum u. dessen Entw. aus d. Brutknospe 

 (Ann. d. Jard. Bot. d. Buitenzorg, IV, 1884), gives an account in detail of the morphology 

 of Psilotum and adds a list of the literature of the group, giving under each work quoted an 

 indication of its scope.] 



