148 GENERAL NATURE Or PLANTS. 



6. When newly formed it is in a very lax state, and posses- 

 ses great powers of absorption ; probably in consequence of 

 the excessive permeability of its membrane, and the imperfect 

 cohesion of its cells, 



7. Cellular tissue, otherwise called Parenchyma, constitutes 

 the soft and brittle parts of plants ; such as pith, pulp, the 

 spaces between the veins of leaves, the principal part of the 

 petals ; and the like. 



8. Succulent plants are such as have an excessive develope- 

 ment of cellular tissue. 



9. It may be considered the most essential kind of tissue, 

 because, while no plants exist without it, many are composed 

 of nothing else. 



10. Tissue is called Woody Fibre when it is composed of slen- 

 der tubes, which are conical and closed at each end, and placed 

 side by side. 



11. Woody Fibre is what causes stiffness and tenacity in 

 certain parts of plants ; hence it is found in the veins of lea ves, 

 and in bark, and it constitutes the principal part of the wood. 



12. Vascular tissue is that in which either an elastic tough 

 thread is generated spirally within a tube that is closed and 

 conical at each end; or rows of cylindrical cellules, placed 

 end to end, finally become continuous tubes by the loss of 

 their ends. 



13. The most remarkable form of vascular tissue is the 

 Spiral vessel, which has the power of unrolling with elasticity 

 when stretched. 



14. Other kinds of vascular tissue are incapable of unrolling, 

 but break when stretched. 



15. Spiral vessels are not found in the wood or bark, and 

 rarely in the roots of plants. 



16." Vascular tissue of other kinds is confined to the root, 

 stem, veins of leaves, petals, and other parts composed of 

 leaves. It is not found in bark. 



17. The common office of the tissue is to convey fluid or 

 air, and to act as the receptacle of secretions. 



18. Cellular tissue conveys fluids in all directions, absorbs 

 with great rapidity, is the first cause of the adhesions that 

 take place between contiguous parts, and is the principal 

 receptacle of secreted matter. 



19. Adhesion will take place at all times during the growing- 

 season, when the cellular tissue of two different parts, or of 

 two different plants, is kept for some time in contact ; but as 

 none but tissues of nearly the same nature will adhere, graft- 

 ing and budding, which are caused by the adhesion of conti- 

 guous parts, can only take place either between different 

 varieties of the same species, or between nearly related 

 species ; and even then only when the corresponding parts of 

 the scion or bud, and the stock, are placed in contact. 



210. Woody fibre conveys fluid in the direction of its length* 



