THE FIBRO-VASCULAR SYSTEM. 



10? 



sues, any of which may be wanting in, or separated a little 

 space from, the bundle. In short, the elementary tissues, 

 particularly tracheary, sieve, fibrous, and parenchymatous 

 tissues, are to be considered as the units, and the term Fibro- 

 vascular Bundle as little more than a convenient expression 

 of the usual condition of aggregation of these units.* 



The general structure of fibro-vascular bundles will be 

 more readily un- 

 derstood after 

 the examination 

 of a number of 

 examples. Those 

 which follow are 

 not in any sense 

 typical ; they are 

 only illustrative. 



136. The fi- 

 bro-vascular bun- 

 dle of the stem of 

 Pteris aquilina 

 is composed of 

 tracheary and 

 sieve tissues, par- 

 enchyma, and a 

 small amount of 

 poorly developed 

 fibrous tissue. In 

 transverse s e c - 



tion the bundle Fig. 96. Part of a transverse section of the fibro-vas- 



, ,, cular bundle of the stem of Pteris vquilina ; , spiral ves- 



liaS Usually ail sel; g, g, scalarifonn vessels ; */>, sieve tissue; 0, fibrous 



alli-rkfi/>al r>n-Hino tissue (protophloem of Russow) ; sg, bundle sheath; p. 



ilt5. starch-bearing parenchyma : K, K, thickened angles of 



The great mass ^wtorm vessels.-After Sachs. 



of the bundle is made up of large scalariform vessels, 

 Avhich occupy its interior (y,g,g, Fig. 96). Enclosed in 

 the scalariform tissue are masses of parenchyma and a few 



* By considering the Fibro-vascular Bundle to be one of the struc- 

 tural units of the higher plants a serious mistake has been made, 

 leading to profitless discussions and speculations as to its typical struc- 

 ture, and diverting attention from the study of its actual structure. 



