iS4 



PART II. VEGETABLE HISTOLOGY. 



the primary circle, the tissue usually consists of parenchyma, 

 which also separates the bundles laterally, but sometimes it 

 contains clusters of stone-cells, c 



masses of sclerenchyma fibers, 

 or even other fibro -vascular 

 bundles, as in the rhizome of 

 Pteris aquilina, Fig. 442. The 

 cortex also usually consists 

 mainly of parenchyma, passing 

 toward the exterior into a thick- 

 walled hypoderma. The type 

 is well illustrated in the rhizome 

 of Aspidium Filix mas. Here 

 the principal bundles, which 

 are from eight to twelve in 

 number, are circularly arranged 

 about a central parenchyma- 

 tous area which contains no 

 bundles. Each bundle of the 

 circle sends thick anastomosing branches to those adjacent to 



c c 



Fig. 442. — Diagram of cross-section of 

 rhizome of Pteris aquilina, showing arrange- 

 ment of tissues ; a, two of the primary circle 

 of fibro-vascular bundles; />, two large cen- 

 tral bundles; c, one of the two dark-colored 

 masses of sclerenchyma fibers; d, hypoder- 

 mal tissue. 



Fig. 443. 



Fig. 444. 



Fig. 443. — Longitudinal view of the rhizome of Aspidium filix mas with the cortical 

 portions cut away to show the cylinder of anastomosing bundles; a, one of the branches of 

 a bundle passing off to a leaf. Magnified about five diameters. Somewhat diagramatic. 



Fig. 444. — Transverse section of rhizome of Aspidium Filix mas, showing arrange- 

 ment of bundles ; a, one of the bundles of the primary circle ; b, one of the branches passing 

 off to a leaf; c, c, places where leaves have been cut away; d, thick-walled hypodermal 

 cells. The unshaded portion is mainly parenchyma. Magnified about five diameters. 



it, so that as a whole they form a netted cylinder. From these, 

 numerous smaller bundles pass outward through the cortex to 

 supply the leaves (Figs. 443 and 444). 



