TUE GREAT TISSUE-SYSTEMS. 115 



Tlie sclerotic pareiiclivnia and the sclerotic i^rosencliviiiu Ijutli 

 arise through a transforniatioii (hardening, ctc.j of portions of 

 originally-soft fundamental parenchyma. In most ])lants ahove 

 the ferns the fundamental system contains neither of these tissues. 



The Flhro-vascular system is composed of loiitrituchnal 

 threads or strands of tissue known as i\nd jihro-vascular hum/les^ 

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

 plants. They appear here and there in the section (Fig. 48,/'.^) 

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

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

 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 Anato:my (Histology) of the Ehizome. 



General Account. Microscopic study of thin sections of the 

 rhizome shows the various tissues to be composed of inmimerable 

 closely-crowded cells, which dilfer 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 dimeusions, 

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

 tion may give an imperfect or entirely false impression of the 

 real form of the cells, — just as the faceof a wall of ma^^oury 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 ha* 

 little scientific value. B\^ many botanists it has been rejected alto^«'ther ; 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 (\v)io first introduced it) and 

 its value for beginners is conceded by De Bary. 



