10 CELLULAR TISSUE. 



creases in size by the deposition of foreign matter, and by this 

 means attains a size much greater than its original dimensions. 



8. Organic mucus exists in the form of a thin homogeneous 

 membrane, covering the cuticle of many plants, and forming a 

 lining to the intercellular passages, or filling them up. It 

 probably exists in all plants, in some form, if in no other than 

 forming the cement by which the tissues are made to cohere. 

 In the young shoot of the Sambucus nigra it is readily observed. 

 Meyen considers the intercellular mucus a secretion of the cells 

 themselves. 



Section 1, — Cellular Tissue. 



9. This tissu€, in its most common form, is composed of 

 minute cells or little bladders, and in the living plant is in a state 

 of greater or less adhesion. Many names have been applied to 

 tissues, made up of the variously formed cells : — 1. Parenchyma 

 (para^ between, and cheuma, effused, tissue). 2. Hexagonien- 

 chyma [hexagonios, six-angled). 3. Sphairenchyma {sphaira^ 

 a sj^here). 4. Merenchyma [tncrtio, to revolve), ellipsoidal cells. 

 5. Ovenchyma (oon, an egg), oval cells. 6. Conenchyma (konos, 

 a cone), conical cells, as hairs. 7. Cylindrenchyma {kulindros, 

 a cylinder), cyhndrical cells. 8. Prismenchyma [prisma, a 

 prism), prismatic cells. 9. Muriform tissue [murus, a wall), like 

 bricks. 10. Pinenchijma [pinax^ a table), tabular or flat cells. 



11. Prosencliyma {i^ros, lengthened out), long, tapering cells. 



12. Colpenchyma (koljjos, a fold), sinuous cells. 13. Claden- 

 chyma [klados, a branch), branched cells. 14. Actinenchyina 

 [aktin^ a ray), star-shaped cells. 15. DcBdalenchyma {daidalos, 

 entangled), entangled cells. Although the walls of the cells, 

 when cut through, appear to be simple membrane, yet, in some 

 cases, they may be separated, and individual cells be exhibited 

 unconnected. If the pith of the elder be cut through with a 

 sharp knife, the cut surface, even under a moderate magnifier, 

 has the appearance of fine honeycomb ; but if a piece be boiled 

 in a weak solution of potash, and then gently rubbed, the cells 

 will separate (which they could not do were the walls of simple 

 membrane), and appear in the form of exceedingly mi- pj^ j 

 nute vesicles, as in Fig. 1. These were the cells that r^ ^ 

 gave the honeycomb appearance to the pith when (JJ \J 

 cut, before boiling. The pressure of the cells on each gimpie 

 other caused the hexagonal appearance, and, when freed *'^^^'- 



8. How does orsranic mucus exist? — 9. Of what is the cellular tissue 

 composed ? How does the pith of the elder appear when cut through ? 

 What causes this appearance ? 



