1 I N VASCULAR CRYPTOGAMS. 



(Fig. 310 A), Kraussiana, and Martensii : and in these cases it has, in transverse section, 



an elongated elliptical form. The first narrow spiral vessels arise nearly in the two foci 



of the ellipse ; from these points two alternating rows of much v»'ider scalariform vessels 



proceed inwards and become very slowly lignified, until a vascular band formed 



from a double row of woody vessels lies within the fibro-vascular bundle. The outer 



much narrower elongated cells of the bundle do not become woody ; they form the 



phloem, the outermost peripheral layer of which consists of much wider cells. In Sela- 



ginella inaqualifolia (Fig. 311), three fibro-vascular bundles lie parallel and side by side 



in the stem, each resembling the single bundles of the species mentioned before. In 



Lycopodium ChamcBcyparissus (Fig. 310 5) a fibro-vascular cylinder occurs in the stem; 



four parallel transverse bands of xylem lie in it, each of which consists of a double row 



of wide scalariform vessels, with narrow spiral vessels also right and left at its ends. 



Each of these transverse bands corresponds in all respects to the single fibro-vascular 



bundle of Selaginella ; the whole of the cylinder in the stem of Lycopodium is therefore 



made up by a coalescence of four fibro-vascular bundles. In the same manner the whole 



of the densely lignified tissue which fills up the interstices of the fibro-vascular bundles 



and forms an envelope to them, is the result of a coalescence of as many layers of 



phloem, each fibro-vascular bundle being enveloped by its own layer. Between each 



pair of transverse bands of xylem lies also a row of wider cells, which may be recognised 



on longitudinal section as sieve-tubes ; the periphery of the whole of the phloem is 



also formed of v/ider cells. It is therefore beyond doubt that the axial cylinder of 



L. Cham(£cy parts sus consists of several coalescing parallel fibro-vascular bundles^. If 



the three bundles in the stem of S. inoequalifolia are imagined laid side by side and to 



have united in growth laterally, they would present a precisely similar structure. In 



Lycopodium Selago there is a similar axial cylinder, but the groups of vessels do not in 



this case form transverse bands, but a more complicated figure in a transverse section ; 



otherwise the arrangement agrees completely with that of L. ChamcEcyparissus {cf. 



Cramer). In L. cla'vatuyn two bands of vessels lie in the tranverse section of the axial 



cylinder, and between them a diametral row of wider cells (sieve-tubes). The outer 



fibro-vascular bundles are curved like a horseshoe : from the concavity which faces 



outwards a group of vessels projects : between the three arms so formed of each of 



these horseshoe-shaped outer bundles lie again two rows of wider cells (sieve-tubes), 



while all the rest of the phloem Vv'hich fills up the space between the fibro-vascular 



bundles consists of very narrow elongated cells. The single fibro-vascular bundle of 



Selaginella has many points of resemblance to that of Ferns {e.g. Pteris aquilma), as 



Dippel has already pointed out ; and this resemblance is only "partially obliterated in 



Lycopodium by the lateral coalescence of several fibro-vascular bundles'^. 



Only one bundle bends out into each leaf, forming, in Selaginella and Lycopodium, 

 an axial bundle through the mid-rib, and, as has been said, uniting with the outer edge 

 of a cauline bundle. 



In Selaginella the fibro-vascular bundles are surrounded by large spaces which contain 

 air, into which transverse rows of cells pass out to the bundle like buttresses from the 

 surrounding fundamental tissue. In Lycopodium these air-cavities are wanting. The 

 fundamental tissue of both genera consists of elongated cells with oblique septa dove- 

 tailed into one another in a prosenchymatous manner. In Selaginella the cell-walls are 

 thin, the cavities wide, and there are no intercellular spaces ; in Lycopodium the walls 

 of the fundamental tissue are usually much thickened, especially in the part that 



' A similar explanation may also be given of the complicated fibro-vascular bundle of the 

 thickish roots of L. clavatum, as described by Nageli and Leitgeb, 



^ I found a stem of Pteris aqtnlina in which the two inner cauline bundles had coalesced later- 

 ally to such an extent as to form a hollow cylinder, enclosing a part of the parenchymatous funda- 

 mental tissue as medulla. 



