132 



PART II. VEGETABLE HISTOLOGY. 



It should also be noted that in the germination of some seeds, 

 as that commonly called Vegetable Ivory, the cell-walls, as well 

 as the cell-contents of the endosperm, are converted into soluble 

 matter, which serves as food for the growing plantlet. 



Thickened cell-walls are seldom homogeneous in structure, 

 but if viewed in cross-section, they have the appearance of being 

 arranged in concentric layers, as in Fig. 368. This is called 

 stratification, and the phenomenon is due to the alternation of 

 more watery layers with less watery ones. Thick-walled cells, 

 like bast fibers, also 



frequently show on 

 the outside delicate 

 lines running trans- 

 versely, obliquely or 

 longitudinally, as 

 shown in Figs. 369, 

 370 and 371. The 

 term striation has 



Fig. 368. 



Fig. 369. 



Fig. 370. 



Fig. 368.— Transverse section of bast fibers from 

 been applied tO this t ^ le stem °f Aristolochia Sipho, showing stratifica- 

 tion. Magnified about 300 diameters. 



Fig. 369. — Portion of a bast fiber, showing oblique 

 striation. Highly magnified. 



Fig. 370. — Portion of bast fiber, showing trans- 

 verse striation. 



Fig. 371. — Bast fiber from the bark of Cinchoni 

 Calisaya, showing longitudinal striae and small 

 tubes connecting the lumen of the cell with the 

 exterior. Magnified about 75 diameters. 



form of marking. In 

 many cases, also, 

 delicate, simple or 

 branching tubes, 



called pore-canals, " Fig. 37 i. 



will be seen running from the cavity or lumen of the cell through 

 the wall, Figs. 368 and 371. They doubtless facilitate the circu- 

 lation of the sap from cell to cell. 



The Protoplasm. Protoplasm exists both in an active and 

 in an inactive condition. In its active state, as found in rapidly 

 growing cells, it exhibits motility and other vital phenomena in a 

 marked degree ; it imbibes large quantities of water, and becomes 

 in consequence, nearly fluid, but as we find it in the cells of 

 seeds, tubers, and thickened roots, it exhibits few signs of vitality, 

 contains comparatively little water, and its condition approxi- 

 mates that of a solid. 



The -words protoplasm and proteid are not synonymous. The 

 former is used in the physiological sense to indicate the living 

 matter of the plant ; the latter is rather a chemical term applied 

 alike to the albuminous matter which makes up the bulk of living 



