130 



PHYSIOLOGICAL BOTANY. 



395. Thus the cell appears to be the type of every form of 

 tissue, the material of which the vegetable fabric is built, and 

 the laboratory where the work is performed. 



Review. 385. What is the simplest form of vegetation ? What constitutes a Tissue T 

 Name the four tissues. 387. What the form of the cells of Parenchyma ? Classify them. 

 ;iS!>. What the form of the cells of Pleurenchyma ? T\vo varieties? 390. In what trees 

 do we find pitted cells? Show them. Explain fig. 474. 391. What is Trachenchyma T 

 How are these tubes made? Show the structure of dotted ducts (480). 3!)3. Office of 

 Cienchyma? 394. Nature of these tubes ? What of intercellular passages ? 395. Give, 

 finally, the import of the cell. 



CHAPTER III. 



THE EPIDERMAL SYSTEM 



Includes the external covering of all herbaceous growths 

 viz., the epidermis, stomata, hairs, glands, cuticle, etc., organs 

 which in older stems give place to bark. 



495 



496 



494 



i91, Cells of epidermis with a stoina from leaf of Helleborus fcetidus. 495, Vertical section of a stoma of 

 Narcissus a, cuticle. 496, Epidermis cells with stomata of Tradescautia Virgiuica. 



396. The epidermis (skin) consists of a layer of united, empty 

 cells, mostiy tabular, forming a superficial membrane. It in- 

 vests all plants higher than Mosses, and all parts save the ex- 

 tremities, the stigma, and rootlets. Its office is to check evapo- 

 ration. That delicate membrane which may be easily stripped 

 off from the leaf of the Houseleek or the garden Iris is the cpi- 



