PART II. VEGETABLE HISTOLOGY, 



longer than broad, and have their ends square or rounded rather 

 than oblique or tapering. Many of the series are thin-walled 

 cells, but others become thickened by cellulose, cutinous or lig- 

 neous deposit. The following are the principal kinds : 



(i) Parenchy7iia proper, or soft tissue, is at once the most 

 abundant and the least modified of all the vegetable tissues. 

 The walls are thin, and frequently, though not always, composed 

 of unmodified cellulose. In form they are commonly spheroidal 

 or polyhedral, and the longitudinal diameter rarely much exceeds 

 the transverse. 



It includes most 

 of the soft tissues of 

 plants, such as the 

 green cells of the 

 leaf, the thin-walled 

 cells of the pith, a 

 considerable por- 

 tion of the cells of 

 the bark, frequently 

 those of the medul- 

 lary rays, etc. Not 

 infrequently the cell- 

 walls are so une- 

 qually thickened as 

 to present the ap- 

 pearance of mark- 



. . Fig. 398. — Parenchyma cells irom the root of Aspidistra, 



ingS Or SCUlptUringS magnified 155 diameters. They are shown in longitudinal 

 r . 1 • j view. 



of various kinds; 



indeed, they are seldom of uniform thickness, but commonly 

 their membranous character and transparency makes them 

 appear so. Forms of pitted parenchyma are shown in Figs. 399 

 and 400. 



The very loosely arranged green cells that occur in the 

 interior of leaves are called spongy parenchyma ; the more com- 

 pactly arranged and somewhat elongated ones found next the 

 upper epidermis of most flattened leaves, are called palisade 

 parenchyma ; parenchyma like that illustrated in Fig. 399, is 

 called pitted parenchyma ; that in which the cells take star- 

 shaped forms, as shown in Fig. 365, is called stellate parenchyma; 



