FILICINEJE. 465 



subterranean shoots) three spiral rows of segments, the segmental walls advancing 

 in the anodal direction, as in many Mosses. The small widely separated leaves, 

 which have no fibro-vascular bundles, are borne upon the angles of the stem and bear' 

 no apparent relation to its branches. 



Psilotum tri'quetrum is a plant perfectly destitute of roots, forming however a 

 number of underground shoots which serve the purpose of roots and are extremely 

 similar to them. On the shoots of the rhizome which approach the surface of the 

 ground may be detected with a lens minute leaves of a whitish colour and acicular 

 shape ; the deeper root-like shoots ha^e a blunter end, on which no trace of leaves 

 can be detected, even with the lens. While the anatomical structure of the super- 

 ficial shoots corresponds to that of the true stem of these plants, in these deeper 

 shoots the vascular bundles are united into an axial group, as in true roots. The 

 shoots which bear visible rudiments of leaves may turn upwards, become green and 

 transformed into ordinary foliage-shoots, while the root-like shoots, which, are more 

 slender, may also turn upwards, become thicker, and assume the appearance of 

 the ordinary superficial rhizome-shoots. In this point therefore they differ at once 

 from true roots, but still more in the absence of a root-cap. They terminate in an 

 apical cell, which forms oblique segments alternating in different directions. The 

 most important point, however, is that these shoots really possess rudiments of leaves 

 which consist of only a few cells and do not project above the surface, but remain 

 concealed in the tissue. They are best recognised in longitudinal section, when 

 they are seen to consist of an apical cell and from two to five cells with the 

 characteristic arrangement of leaf-cells. Similar rudimentary leaves consisting of 

 but few cells occur also on the ordinary rhizome-shoots, where, however, they do 

 not undergo further development, especially when the end of the shoot appears 

 above ground. The root-Uke shoots branch like the ordinary ones ; a cell is /;ut 

 off by an oblique wall from one of the youngest segments, and forms the apical 

 cell of the new shoot. 



The other genera all possess true roots. In the Lycopodieae with creeping 

 or climbing stems they arise singly and dichotomise in rectangularly intersecting 

 planes in the soil. It has already been mentioned that in the Lycopodieae witn 

 erect stems, such as in Z. Selago^ Phlegviaria, ulicifolium, the roots issue in a tuft 

 from the base of the stem which is somewhat tubercular. These roots originate high 

 up in the stem, as high as five centimetres and even above the first bifurcation 

 according to Strasburger ; they develope at the periphery of the axial fibro-vascular 

 mass, but they are peculiar in that they grow down through the fundamental tissue of 

 the stem and even dichotomise there. (Compare with Angiopteris, p. 417.) 



The Sporangia, in the genus Lycopodiuvi, occur singly on the bases of the 

 leaves or in their axils. As in all Dichotomeae, they are here larger than in the 

 Ferns. They are borne on short broad stalks, and the capsule is somewhat reniform,. 

 its longer axis lying transversely to that of the leaf. They open by means of a slif 

 running in this direction over the apex, two valves being formed which remained 

 united at the base. The contained spheroidal or tetrahedral rather small spores are 

 numerous ; they all have the same shape and are provided with a sculptured exospore. 

 After I had pointed out in the first edition of this book (1868) that the sporangia of 

 the Lycopodieae originate as multicellular protuberances of the tissue pf the leaves,. 



Hh • 



