THE FIBRO-VA8CULAR SYSTEM. 



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 "C^ 

 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 

 has usually an 

 elliptical outline. 



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

 cular bundle of the stem of Pleris nqmlina ; , spiral ves- 

 sel; y, g, scalariform vessels ; fp, sieve tissue: A, fibrous 

 tissue (protophloem of Russow) ; sg, bundle isheath; p y 

 ' 



, y 



et arch-beanng parenchyma: A', K, thickened angles of 

 The great mass scalariform vessels.-After Sachs. 



of the bundle is made up of large scalariform vessels, 

 which occupy its interior (g, 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 hag been made, 

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

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



