4 8 



PHYSIOLOGY. 



gases in the plant become rarefied as a result of the excessive loss of water. 

 There are then successive rows of air or gas bubbles in the vessels separated 

 by films of water which also line the walls of the vessels. The condition of 

 the vessel is much like that of a glass tube through which one might pass the 

 "froth " \vhich is formed on the surface of soapy water. This forms a chain 

 of bubbles in the vessels. This chain has been called Jamin's chain because 

 of the discoverer. 



109 Why water or food solutions can be raised by the plant to the height 

 attained by some trees has never been satisfactorily explained. There are 

 several theories propounded which cannot be discussed here. It is probably 

 a very complex process. Root pressure and transpiration both play a part, 

 or at least can be shown, as we have seen, to be capable of lifting water to a 

 considerable height. In addition to this, the walls of the vessels absorb water 

 by diffusion, and in the small vessels capillarity comes also into play, as 

 well as osmosis. 



110. Synopsis of tissues. 

 Epidermis. 



Epidermal 

 system. 



Trichomes 

 (hairs). 



Fibrovascular 

 system. 



Xylem. 



Phloem. 



Fundamental 

 system. 



Simple hairs. 

 Many-celled hairs. 

 Branched hairs, often stellate. 

 Clustered, tufted hairs. 

 Glandular hairs. 

 Root hairs. 

 Guard cells of stomates. 

 Spiral vessels. 

 Pitted vessels. 

 Scalariform vessels. 

 Annular vessels. 

 Wood fibers. 

 Wood parenchyma. 

 Cambium (fascicular). 

 f Sieve tubes. 

 Bast fibers. 

 Bast parenchyma. 

 Cork. 

 Parenchyma. 



Ground tissue. 

 Interfascicular cambium. 

 Medullary rays. 

 Bundle sheath. 



Schlerenchyma (thick-walled cells, in nuts. etc). Collen- 

 chyma (thick-angled cells, under epidermis of succulent 

 stems). 



