MOKPHOLOGY OF STEMS. 



always associated with the wood-cells, so that they are in a general 

 way taken together as constituting the wood, or woody tissue, and 

 as forming what is more definitely termed fibro- vascular tissue or, 

 when distinguishable into threads, fibro-vascular bundles. These 

 run lengthwise through the stem, sometimes as such separate 

 threads, sometimes confluent into a compact structure. The 

 softer or at least the non-fibrous portions, formed of comparatively 



a b d e fa 



A 





short and commonly thin-walled cells, form cellular tissue. Its 

 ordinary form (of roundish, cubical, or polyhedral and thin-walled 

 rells) is called parenchyma. This abounds in herbaceous stems or 

 herbaceous parts: in trees and shrubs, woody tissue largely pre- 

 vails; in most herbs, it forms a notable portion ; in some (especially 



FIG. 125. Fibro-vascular elements, a. Bast-cells (long wood-cells) of fibrous bark 



of Linden <>r p.ass-wood. It. Some wood-cells and (lirlowla duct, and r a detached 

 wood-cell of the wood of same tree, equally magnified \\itli <i. d. A detached wood- 

 eel! from a shaving of White Pine, showing the peculiar disk -like markings. <. Portion 

 of same shaving. ./'. Portion of a dotteil duct from the Vine, evident ly made np of a 

 series of short cells. ;/. Part of a smaller dot ted duct , showing no appearance of such 

 eoiii|ici.sjijon. /), i. Spiral ducts or vessels, of the ordinary kind. j. Spiral duct of 

 P>anana. /.'. Due! from Celery, the thread within spiral or annular In low, reti. nlated 

 aliovc. and higher passing into the state of dotted duct. /. Duct from Impaticns, with 

 Hi.' open spiral passing into rin;;s at the middle. All magnilied somewhat equally. 



