68 



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 definitel}* 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 f g 



A 



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

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

 cells) 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. 126. Fibro-vascular elements, a. Bast-cells (long wood-cells) of fibrous bark 

 of Linden or Bass-wood, b. Some wood-cells and (below) a duct, and c. a detached 

 wood-cell of the wood of same tree, equally magnified with a. <1. A detached wood- 

 cell from a shaving of White Pine, showing the peculiar disk-like markings, e. Portion 

 of same shaving. /. Portion of a dotted duct from the Vine, evidently made up of a 

 series of short cells, g. Part of a smaller dotted duct, showing no appearance of such 

 composition, h, i. Spiral ducts or vessels, of the ordinary kind. j. Spiral duct of 

 Banana, k. Duct from Celery, the thread within spiral or annular below, reticulated 

 above, and higher passing into the state of dotted duct. /. Duct from Impatiens, with 

 the open spiral passing into rings at the middle. All magnified somewhat equally. 



