12 STRONG DRINK AND TOBACCO SMOKE. 



Groups of any or of all these forms of vessels (Plate 

 1, figs. 7 — 11) are known as vascular tissue, as dis- 

 tinguished from the ceUular tissue above described. 



The continuous growth of a plant is generally ac- 

 companied by the formation of wood ; that is to say, 

 much of the cellular tissue is supplanted by tougher 

 and more unbending material, more suitable for the 

 support of the plant during growth. These Avoody 

 parts are mostly composed of long Jihrous cells with 

 thick walls. Fig. 12 represents one of them pointed 

 at both ends, and fig, 13 another with nearly square 

 ends. They occur in abundance in herbaceous plants, 

 and in all wood knit together into a tissue, such as is 

 seen at fig. 14. When united in one tissue with the 

 vessels before described, the comj^ound tissue is called 

 Jihro-vasciilar. 



A common deal shaving exhibits, under the micro- 

 scope, a tissue composed of long cells pointed at both 

 ends, and having on their sides pits, or cup-shnped 

 depressions (fig. 15), which in two individual cells are 

 fitted face to face, and thus form a cavity for the 

 reception of the resinous matter which we smell so 

 perceptibly in freshly-cut deal, or in newly-planed deal 

 shavings and sawdust. 



A curious form of the fibrous cell is, according to 

 some authors, found in bark (figs. 16, 17), some being 

 Ijranched. Fig. 18 is another form of fibrous cell, also 

 found in bark, and like some cells dotted. In inner 

 coats of seeds are commonly found minute, elonoated 



