2,26 



THIRD GROUP. VASCULAR CRYPTOGAMS. 



Several concentric rings of bundles are found in a number of fern-stems with many 

 rows of leaves, as in Pteris, in species of Saccoloma, in the Marattiaceae and Cera- 

 topleris. Pteris aquilina is one of this number. In its underground stem are seen an 

 upper and a lower bundle (the two long central ones at ig in Fig. 179), and this vascular 

 bundle-cylinder is strengthened by a cortical system of many accessory bundles (Fig. 

 *79 a g)' The young plant has an axile crescent-shaped vascular bundle up to the 

 time of the formation of the seventh and ninth leaves, then the stem forks. As 

 the branches increase in thickness the course of the bundles alters. The axile 

 bundle divides into an upper and under one, and thus the upper and lower bundles are 

 formed, and these split up by forking into slenderer branches which soon unite again 

 (Fig. 179 B, J/, st}. When the branches are about six centimetres long and four milli- 

 metres thick, weaker branches are given off from the two bundles, and these pursue 

 their course through the cortex near the surface, where they form a net-work with long 



f 



FIG. 180. Cyathea Imrayana ; transverse section through 

 the fresh stem, nat. size. All the quite black bands and points 

 are sections through sclerenchyma, all the lighter through 

 vascular bundles. In or near the leaf areas, especially b and 

 d, are root-bundles going to the periphery ; f small pits of the 

 base of the leaf, a vascular bundle of the main tube, s outer, 

 s> inner plate of its sclerenchymatous sheath. Inside s' the 

 pith, outside s the cortex, with their small bundles. From De 

 Bary, Vergl. Anat. 



FlG. 181. Piece of a fresh stem of Cyathea Imrayana 

 with the bases of four leaf stalks after peeling off the outer 

 layers of the cortex, seen from without. The margins of four 

 foliar gaps, the bundles which spring from them and go into 

 the leaves with the rudimentary roots (black) rising on them, 

 and the small bundles which descend in the cortex, are laid 

 bare ; the latter and the roots are quite free, the other parts 

 are still covered by some transparent parenchyma, through 

 which they are clearly seen, and which holds all the parts 

 together in their natural position. Natural size. From De 

 Bary, Vergl. Anat. 



narrow meshes, the upper middle strand (Fig. 179 A, ag] of which is distinguished 

 by its size. The rhizome retains this structure when fully grown ; the peripheral net- 

 work of bundles is separated from the cylinder formed by the upper and lower bundles 

 by two stout plates of brown sclerenchyma (Fig. 179/f). Branch-bundles pass from 

 both net-works into the branches and leaves, into the roots only from the outer. 



Cyathea Imrayana (Figs. 180 and 181) may serve as an example of the occurrence of 

 bundles in the pith and cortical tissue along with the simple vascular cylinder. Those 

 in thfe cortex proceed from the bundles which pass into the leaf, those in the pith from 

 the foliar gaps. 



