STRONG DRINK AND TOBACCO SMOKE. 11 



In the growing parts of plants are found, in all stages 

 of developnient, long tubes or vessels. These, in many 

 instances, are seen to be formed by a series of cells 

 placed one above another (Plate 1, fig. 6), their ends 

 becoming finally obliterated, when they form canals or 

 vessels, such as are represented at fig. 7, having their 

 walls dotted. This description of vessel is called a 

 dotted duct, and is very common in the roots of many 

 plants, such as chicory. 



Vessels, like cells, have their walls lined internally 

 with a deposit. Fig. 8 represents one of them with 

 such a deposit, in the form of a fibre wound spirally 

 on its wall, the fibre having become stretched by the 

 elongation of the vessel. 



Beautiful examples of spiral vessels occur in the veins 

 of leaves (fig. 9) ; they are abundant in the stem of the 

 strawberry plant, and are readily seen by passing a 

 knife-blade gently round the stem, and then dividing 

 it by gradually drawing the parts asunder. The fine 

 threads thus obtained, when examined under the micro- 

 scope, will be found to consist of spiral vessels, with 

 the fibres more or less unrolled at their extremities. 



Another very common form of vessel (fig. 10) is 

 known as 7'eticulated, owing to the broken irregular 

 form which the deposit assumes. 



Fig. 1 1 represents portions of three vessels taken 

 from the stem of the vine. These are called scalari- 

 form ducts, owing to the deposit being formed in bars, 

 similar in appearance to the rungs of a ladder. 



