288 PRlMARy ARRANGEMENT OF TISSUES. 



Their creeping rhizome shows a circle of bundles in transverse section. Of 

 these, one passing along the middle of the upper side (the upper bundle, o Figs, 134, 

 135) and a second passing similarly along the under side (the lower bundle, u) are 

 distinguished by their band-like form and greater size from the other weak ones, which 

 are opposite to the two rows of leaves. Both the stronger bundles are connected 

 regularlv, at distances corresponding to those separating the leaves, by transverse 

 bundles curved convexly upwards, or bent at an angle, so as to form a net, the 

 meshes of which are the foliar gaps. From the margins of these arise (in addition 

 to the bundles for the lateral shoots x) the foliar bundles (b) which converge opposite 

 the point of insertion of the leaf, which is usually relatively small, and run almost 

 radially perpendicular in the stem up to that point : these bundles may anastomose 

 one with another, and with the upper and lower bundles by solitary thin transverse 

 connections. The transverse sections of the foliar bundles are the small bundles 

 seen in the transverse section of the stem ; they there form together with the 

 upper and lower bundles either a circle, as above stated, or in flattened stems 

 an elliptical figure, which is often compressed in such a way that the upper and 

 lower bundles have a central position, while the foliar bundles are outside. 



The arrangement described occurs in a simple form, with specific modifications 

 as regards the number of the foliar bundles, the form of the gaps, strength of the 

 bundles, &c., in Asplenium obtusifolium, A. resectum, Acrostichum brevipes, A. 

 Lingua, A. simplex, A. INIelanopus, Polypodium altescandens, P. tenellum, Nephro- 

 lepis ramosa, Aspidium albopunctatum, A. coriaceum (Fig. 135). In the Davallias 

 there arises the further complication, that the branches springing from the margin of 

 the foliar gap do not run directly or with unimportant anastomoses to the leaf, but 

 first form a network of fine bundles, which stretches over the foliar gap, and sends 

 a certain number of branches into the leaf. According to the number of these foliar 

 bundles (which varies according to the species) the network is simpler (D. parvula, 

 pedata, heterophylla), or more complicated, and with more numerous meshes (D. 

 bullata, dissecta (Fig. 134), elegans, pyxidata, canariensis, &c.). 



A more considerable deviation from the structure described appears in other 

 creeping stems of Ferns with leaves in two rows : here, not only is the foliar gap 

 covered in by a network of bundles, but also instead of the lower bundle two or 

 more reticulately anastomosing bundles are present, and the lower bundle is as it 

 were split up into a network of bundles (Fig. 136). Where the number and arrange- 

 ment of the bundles are very simple, as e. g. in Polypodium aurisetum, piloselloides, 

 cayennense, or where the upper and lower bundles and their transverse connections 

 bordering on the foliar gaps are strongly distinguished from the rest by their size, as 

 in Platycerium alcicorne, the structure may be referred easily to the scheme with 

 upper and lower bundles. But often the upper and lower bundles and all the anas- 

 tomoses are of such uniform strength, and the meshes of different order so irregular, 

 that the foliar gaps can only be distinguished at both sides of the upper bundle, 

 where the bundles pass out into the leaves. In place of the tube regularly per- 

 forated by foliar gaps there is in extreme cases as it were a complex irregular net- 

 work, the relations of which to the more simple type can only be recognised 

 as indicated by the regularly alternating ' foliar meshes ' b. As extreme examples 

 may be named, Polypodium vulgare, sporadocarpum, aureum ; numerous species of 



