a84 PRIMARV ARRANGEMENT OF TISSUES. 



Lygodium^, and also of Schizsea, and the leafless stolons of Nephrolepis. The 

 bundle has usually a circular transverse section, in Salvinia rotundifolia it is horse- 

 shoe-shaped. 



Sect. 8i. In many Ferns the original axile bundle widens out as the stem grows 

 stronger into a tube, which is for the most part closed all round, and has only at 

 each node, below the insertion of the leaf, a relatively small slit ox foliar gap, through 

 which the medullary parenchyma is connected with the cortex, and from the margin 

 of which one or several bundles pass into the leaf. To this series belong for the 

 most part forms with a thin creeping rhizome, and leaves alternating in two rows : 

 the investigated species of Marsilia, normal specimens of Pilularia globulifera " with 

 a very small foliar gap, from the lower margin of which a foliar bundle arises. Most 

 species of Dennstaedtia (D. tenera, scandens, davallioides, punctilobula) have a tube, 

 which is closed as far as the foliar gap ; the bundle which enters the leaf arises from 

 the whole margin of the gap as a continuous concave plate, which is only occasion- 

 ally split up at its base for a certain distance into several bundles lying side by side. 

 ' The same structure is found in all species of Microlepia and Hypolepis, in the 

 species of Phegopteris, which are allied to the latter genus, and in the species of 

 Pteris of the section P. vespertilio, aurita;' further in Polypodium Wallichii, and 

 conjugatum, to the bundle-tube of which attention was first drawn by R. Brown, 

 and in which a bundle passes into the leaf from each side of the narrow slit-like 

 foliar gap '- Of the Hymenophyllaceae, Loxsoma has a closed tubular bundle *, the 

 foliar gaps of which have not been described. Of the Schizseacese " the species of 

 Schizsea may perhaps be mentioned here : but for reasons which will be given below 

 (Sect. 1 06) Russow has correctly placed them in our previous category: otherwise 

 they have been as yet but little investigated. Among the Ophioglossaceae the above 

 described structure occurs in the rhizome of Botrychium Lunaria*. Hofmeister' found 

 in Ophioglossum vulgatum the network of bundles of the rhizome, which belongs 

 to the next category, sometimes coalescent for a certain distance to form a closed 

 tube. 



SicT. 82. Most Ferns with an ascending or upright rhizome or stem, with leaves 

 in many rows, and but shghtly elongated internodes, are distinguished fundamentally 

 from the type just described in this point only, viz. that the foliar gaps are relatively 

 large, and the bands of the bundle-tube, which separate them, are relatively narrow. 

 The tube has accordingly the form of a Net, the meshes of which are the foliar gaps. 

 From the margins of the meshes branch the foliar bundles, which there run obliquely 

 upwards through the cortex to the insertion of the leaf. The bundles of the meshes 

 of the stem are, according to the species, relatively narrow, of round or elliptical 

 transverse section, or, as in stems of the Cyatheacese, broad, or' band-shaped 

 plates, with their margins often curved outwards : the bundles which pass into the 

 leaf show the same varieties of form : their number for each leaf is constant within 

 jiarrow limits in the mature plant of each species, but varies in different species 



Russow, /. c. 2 Russow, /. c. 3 Mettenius, Angiopteris. p. 544. 



* Mettenius, Hymenophyllaceae, p. 418. 

 = [Comp. Prantl, Morphologie d. Gefasskryptogamen, Heft 2, Leipzig, i88l.1 

 Russow, /...p. 1 1 7, &C. 7 Lt, TTT 



' Beitr. III. p. 664. 



