FILICINEAE.—HOMOSPOROUS FIUCINEAE. 



225 



comparatively narrow. To this class belong the many species of the Polypodiaceae, of 

 which Aspidium Filix-mas may serve as an example. A like arrangement is found in 

 the Ophioglosseae which will be described further on. E in Fig. 158 shows the net- 

 work of bundles with the large foliar gaps of an older stem ; each leaf receives several 

 bundles from the edge of its gap. The transverse section in Fig. 177 shows the net- 

 work of bundles forming a circle, and outside of it in the rind the smaller bundles 

 which pass obliquely upwards into the bases of the leaves. The conditions are more 

 simple in the young plant ; the leaf-trace bundles are here united at first in the stem 

 into a solid axile bundle ; then the stem increases in thickness and the formation of 



Fig. 177. Aspidium h'iUx-mas, 

 Transverse section through a strong 

 stem with a pliyllotaxis of 8'2i. From 

 De Bary, VergI, Anat. 



Fig. 179. Pteris aqiiilina. A transverse section of the 

 stem; r its brown epidermis with a layer of scltrenchyma 

 beneath it ; / colourless soft parenchyma of the fundamental 

 tissue, pr brown layers of sclerenchyma of the fundamental 

 tissue, zv inner vascular bundles (upper and lower bundles), ag 

 upper broad middle strand of the outer network. B isolated 

 upper middle strand of the outer (cortical) network st and its 

 branches st' and st" ; b bundles of the leaf stalk, aa outline of 

 the stem. Natural size. 



Fig. 178. Aspiditim cana- 

 ceiim, rhizome slightly magnified. 

 A system of vascular bundles in 

 the cylinder laid out flat. B trans- 

 verse section, o upper bundle, 

 11 lower bundle, both conspicuous 

 in the transverse section from 

 their greater breadth. After 

 Mettenius. 



the reticulated vascular bundle-cylinder begins ; at this stage each leaf receives a 

 single bundle from the lower angle of the foliar gap ; in the second year the leaves 

 receive several bundles from the edge of the foliar gap, and the number may be as 

 high as seven in vigorous full-grown stems. In horizontal stems with two rows of 

 leaves foliar gaps are found placed alternately right and left on the lateral faces of 

 the stem. A transverse section shows a circle of bundles ; one of these bundles runs 

 along the upper or dorsal side and one along the under or ventral side ; they are more 

 developed than the others and are known as the upper and lower bundle. 

 [2] 



