THE GREAT TISSUE-SYSTEMS. 115 



The sclerotic parenchyma and the sclerotic prosenchyma both 

 arise through a transformation (hardening, etc.) of portions of 

 originally-soft fundamental parenchyma. In most plants above 

 'the ferns the fundamental system contains neither of these tissues. 



The Fibro-vascular system is composed of longitudinal 

 threads or strands of tissue known as ihejibro-vascular bundles, 

 and these in one form or another are characteristic of all higher 

 plants. They appear here and there in the section (Fig. 48, f.b) 

 as indistinct, pale or silvery areas of a roundish, oval, or elon- 

 gated shape. Closely examined they show an open texture, en- 

 closing spaces which are sections of empty tubes, or vessels and 

 fibres, from which the bundles take their name. 



The Epidermal system consists of a single tissue, the epider- 

 mis, which covers the outside of the rhizome. 



By a simple dissection of the stem with a knife the sclerotic 

 prosenchyma and the fibro- vascular bundles may be seen to be 

 long strands or bands, coursing through the softer fundamental 

 tissues. 



It should be clearly understood that these three systems are, 

 in general, not single tissues, but groups of tissues which are 

 constantly associated together for the performance of certain 

 functions. * 



MICROSCOPIC ANATOMY (HISTOLOGY) OF THE EHIZOME. 



General Account. Microscopic study of thin sections of the 

 rhizome shows the various tissues to be composed of innumerable 

 closely-crowded cells, which differ very widely in structure and 

 in function. In studying these cells the student should not lose 

 sight of the fact that they are objects having three dimensions, 

 of which only two are seen in sections. And hence a single sec- 

 tion may give an imperfect or entirely false impression of the 

 real form of the cells, just as the face of a wall of masonry may 

 give only an imperfect idea of the blocks of which it is built. 



* This classification of the tissues is only a matter of convenience, and Las 

 little scientific value. By many botanists it has been rejected altogether ; but 

 no apology for its use need be made by those who, like the authors, have 

 found it useful, so long as it is defended by Sachs (who first introduced it) and 

 its value for beginners is conceded by De Bary. 



