48 PLANT LIFE. 



Permanent Tissue is the name given to any tissue in 

 which the cells have ceased to divide, and have assumed a 

 permanent form. 



In the higher or vascular Cryptogams and Phanerogams 

 the various tissue-systems are present in the following 

 order. 



Epidermis^ a tissue usually consisting of a membrane 

 composed of a single layer of cells continuous over the 

 exterior of every portion of the plant growing in the air. 



Fibro-vascular System, present in the substance of the 

 plant in the form of one or more comparatively firm strands. 



Fundamental Tissue, forming a groundwork mostly of 

 parenchyma, filling up the spaces between the fibro-vascular 

 bundles and the epidermis. 



Epidermis. — As already stated, the most important 

 function of this tissue is to prevent undue evaporation of 

 water from those portions of plants surrounded by air. In 

 aquatic plants, and those portions of terrestrial plants sur- 

 rounded by a damp medium, as roots, the epidermis is 

 comparatively imperfect or absent. 



In such simple terrestrial plants as Fungi and Lichen- 

 fungi, we are introduced to more or less differentiated 

 structures, which fulfil functionally to a certain extent the 

 work of a true epidermis. In many of the large fungi of 

 the "toadstool" type, the outermost layer of the "cap" or 

 pileus, which consists of densely compacted filaments, due 

 to partial gelification of their walls, become cemented 

 together and form a thin, frequently separable skin, whereas 

 in many Lichen-fungi, the filaments of the fungal portion 

 combine towards the exposed surfaces to form a compact 

 structure called the cortex, resembling a parenchymatous 

 tissue, but as this is formed by the anastomosing and 



