292 



PRIMARY ARRANGEMENT OF TISSUES. 



pass on further in the midtlle, sometimes at the periphery of the pith, and some 

 insert themselves at an acute angle on similar branches from lower leaves, others end 

 blind. At the foliar gap the bundles, which are themselves about as thick as a 

 bristle, are surrounded by brown sclerenchyma, or supported by it on one side, and 

 these sheaths of sclerenchyma, which are closed or open on one side, accompany the 

 bundles for a long distance downwards; sometimes they also anastomose with 



' &l 



Fig. 139. — Cyathea Imrayana ; 

 natural size. From a dead stem, the 

 soft parts of which had rotted away ; 

 the stem is halved longitudinally, 

 and seen from within. The figure 

 shows a piece of the tube of vascu* 

 lar bundles with one foliar gap, / — /, 

 and a leaf-scar exactly halved longi- 

 tudinally. From this t'le bundles of 

 sclerenchyma which accompany the 

 vascular bundles may be seen to 

 branch off, and from there those 

 which accompany the medullary 

 bundles arise as branches and pass 

 down into the pith with many 

 branchings and anastomoses; some 

 of them have blind pointed endings; 

 the one which extends furthest 

 downwards has anastomosed with 

 one coming from a lower leaf. Of the 

 bundles which end at the leaf-scar, 

 wi originates from the pith, the rest 

 from the margin of the foliar gap. 



Fig. 140.— Cyathea imrayana; axile longitudinal section through 

 the same stem as Figs. 141 and 142 ; natural size. The section is about 

 3mm. thick, and for the most part transparent; the black bands of 

 sclerenchyma and/«/^ vascular bundles here represented in one plane 

 do not all He exactly in4his p!ane, but are all near it. Certain parts of 

 the chief sclerenchymatous-sheath s — s' which show through, and at 

 the bottom two portions of the surface of the stem seen obliquely, are 

 shaded off as they pass from the surface of section. The letters a, s, 

 j'.yhave the same meaning as in Fig, 141 ; r cortical bundles, b leaf- 

 scars, d/ vascular bundles passing out into leaves, 70 insc' tions of roots, 

 m a foliar bundle running into the pith ; above X blind ending of a 

 medullary bundle (examined under the microscope). 



similar sheaths, which descend from leaves side by side with or below them, some- 

 times they diminish downwards and end blindly in a -point, while the vascular bundles 

 continue their downward course alone beyond these endings (comp. Fig. 140). 



