148 ACADEMIC BOTANY. 



PART THIRD.— PHYTOTOMY, OR PLANT 

 ANATOMY. 



LESSON XXIX. 



CELLS— FIBRES— VESSELS. 



360. Tissues. 361. Osmose. 362. Spaces. 363. Cell-shapes; 364. 

 Cell-sizes; 365. Cell-markings. 366. Cellular tissue. 367. Fibrous 

 tissue. 368. Vascular tissue. 369. Laticiferous Vessels. 370. Tissue- 

 Systems. 



360. Tissues. — All plants are essentially the same in 

 material structure ; the cells, however, vary in size, shape, 

 texture, and arrangement. The first cells of a phanerogam 

 (Fig. 215, B) are identical with the Red Snow (Fig. 11); 

 but the Red Snow never rises above the condition of a 

 single cell; whereas the higher plants multiply their cells 

 indefinitely and combine them into tissues, which are called 

 Cellular, Fibrous, and Vaseular. 



361. Osmose. — All cell-walls are closed in living tissues; there is 

 no opening from one cell to another ; yet the sap and all the juices of 

 the plant flow through them under the law called Osmose (Gr.-). This 

 is the mutual attraction of two fluids of different densities, by which 

 each passes through a separating membrane until both acquire the 

 same density. 



362. The Spaces between the cells, when small and irregular, are 

 called Intercellular Spaces (Pig. 215, A). When large, they are called 

 Intercellular Passages ; also Lacunes, from the Gr. lakos, a hollow ; 

 L. locus, a lake (Fig. 215, D). Their chief function is air-circulation ; 

 they communicate with the outer air through the pores of the bark 

 and the leaves. 



