24 AEKANGEMENT OF VEGETABLE TISSUES. 



2. Pitted Cellular Tissue ; cells formed ty membrane, which has heen un- 



equally thickened in such a way as to leave rounded depressions at 

 regular intervals. 



3. Fibrous Cellular Tissue (Inenchyma) ; cells formed by membrane and fibre ; 



occasionally formed by fibre alone. 



a. Spiral Cells, with a complete spiral fibre inside. 



b. Dotted Cells, with opaque spots, which are isolated portions of fibre. 



B. — Vascular or Tubular tissue (Angienchyma), composed of cylindrical tubes, 

 which are more or less continuous, and usually overlap each other, or 

 are united by broad oblique extremities. 

 I. Membranous Vascular Tissue ; tubes formed by membrane alone, of varying 

 thickness, but without markings on it. 



1. Ligneous Tissue (Pleurenchyma), composed of fusiform tubes with thick- 



ened walls. 



2. Laticiferous Tissue (Cinenchyma), composed of tubes which anastomose, 



often present irregular dilatations, and convey a peculiar fluid, called 

 Latex ; this tissue may be formed by intercellular canals lined with a 

 continuous membrane. 

 n. Pitted Vascular Tissue ; tubes formed by membrane, with markings of a 

 more or less circular form on their walls. 



1. Pitted Vessels (Bothrenchyma or Taphrenchyma) ; large pitted tubes 



usually ending in broad extremities, the markings on their walls de- 

 pending on internal depressions. This tissue sometimes exhibits con- 

 tractions at regular intervals, as if formed of cells placed end to end, 

 and then is called Moniliform, or Beaded (Articulated Bothrenchyma). 



2. Punctated Vessels (Glandular Woody Tissue) ; fusiform woody tubes, 



the markings on the walls depending on external depressions, and pre- 

 senting the appearance either of single or double, circular discs. 

 Iir. Fibro-Vascular Tissue, composed of tubes in which the thickening matter 

 is deposited in the form of spiral fibres, rings, bars, or dots. 

 a. Perfect Fibro-Vascular Tissue, composed of tubes, in which there is a 

 complete spiral fibre. _ 



1. Spiral Vessels (Tracheae, Ti-achenohyma), in which the spiral fibre is 



elastic, and may be unrolled. 



2. Closed Spiral vessels, or closed Trachese, in which the spiral fibre is 



brittle, or its coils so united to each other, and to the membrane, 

 that they cannot be unrolled. 

 h. Imperfect Fibro-Vascular Tissue, composed of tubes marked by rings, 

 lines, or dots, but without a complete fibre inside. 



1. Annular Vessels or Ducts, having fibres in the form of detached rings, 



which are occasionally united by portions of fibre. 



2. Eeticulated Vessels, having fibres which cross each other, or are disposed 



so irregularly as to form a network. 



3. Scalariform Vessels, having their walls marked by isolated portions of 



fibre, in the form of ladder-like bars. 



4. Dotted Vessels, having their walls marked by isolated portions of fibre 



in the form of opaque dots or points. 

 Any of the vessels included under the Fibro-vascular tissue may exhibit con- 

 tractions at regular intervals, so as to become moniliform. 



