CHAPTER II. — PLANT TISSUES. 



I6 5 



immediately underlying and supporting the epidermis of some 

 plants, as that of the stems of many Monocotyledons and Ferns ; 

 and the fibrous strengthening cylinder sometime found imbedded 

 in the parenchyma of stems considerably beneath the epidermis 

 and outside of the fibro-vascular bundles, as in the stem of the 

 Pumpkin. "The term "bast-fibers" may, therefore, be legiti- 

 mately applied to all these, and in this sense is used in this work, 

 though many authors limit the term to the fibers found in the 

 bast, and call all lignified, fibrous elements, wherever found, scler- 

 otic hy ma fibers. According to 

 this usage, bast-fibers, wood- 

 cells, wood-tracheids, etc., are 

 only varieties of sclerenchyma 

 fibers. 



Fig. 425. 



Fig. 426. 



FlG. 425.— Transverse section of bast cells from the stem of Menispermum canadense. 

 The middle lamella is shaded dark, and the walls of the thickened- fibers show concentric 

 lamination. Magnified about 400 diameters. 



Fig. 426. — Longitudinal view of small portions of the long bast fibers from the stem of 

 the same plant, showing oblique markings in the cell walls. Magnified about 400 diameters. 



Associated with bast-fibers are sometimes found shorter 

 blunt-ended cells which otherwise resemble them. These are 

 often called rod or staff cells, and they may be regarded as inter- 

 mediate in their character between bast-cells and stone-cells. 

 In fact, every gradation may be observed between them. 



HI. — Sieve Series. This includes the different varieties of: 



Sieve Cells or Cribiform tissue. This tissue is seldom formed 



elsewhere than in the phloem or bast-region of fibro-vascular 



bundles. It consists usually of elongated, thin-walled and blunt, 



or somewhat oblique-ended cells, which have areas with sieve- 



