THE GREAT TISSUE-SYSTEMS. 73 



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 tissues known as the fibro-vascular bundles, and 

 these in one form or another are characteristic of all higher 

 plants. They appear here and there in the section (Fig. 35, f.lj] 

 as indistinct, pale or silvery areas of a roundish, oval, or elongated 

 shape. Closely examined they have an open texture, enclosing 

 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 the sclerotic prosenchyma 

 and the fibre-vascular bundles may be seen to be long strands or 

 bands, coursing through the softer fundamental tissues. 



It should be clearly understood that the three systems are 

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

 constantly associated together for the performance of certain 

 functions.* 



MINUTE ANATOMY (HISTOLOGY) OF THE RHIZOME. 



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 section 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. For this reason 

 many of the cells can only be understood by a comparison of 



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

 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 DC Bary. 



