THE OROUPB OF TISSUES, OB TISSUE-SYSTEMS 53 



cheary portion is surrounded by a layer of elongated, thin- 

 walled tissue ■which is, at least in part, a sieve-tissue. In 

 this and allied species the bundles are curiously isolated 

 from the surrounding ground-tissues of the stem. 



Fig. 35.— Magnified cross-section of the stem of a smaller Club-moss 

 (Selaginella inEequifolia), showing three bundles. 



90. The fibro- vascular bundle of the underground stem 

 of the common Brake-fern (Pteris) is composed of trache- 

 ary, sieve, and soft tissues and a small amount of poorly 

 developed fibrous tissue. In transverse section the bundle 

 has usually an elliptical outline. The great mass of the 

 bundle is made up of large scalariform vessels, which 

 occupy its interior (ff, g, g, Fig. 36). Enclosed in the sea- 



