353 ELEMENTARY ORGANS. CHAP. III. 



and ascending the stem in a parallel direction, 

 separating and entering the branches, buds, and 

 foot-stalks ; separating again and distributing them- 

 selves in smaller bundles so as to form the nerves 

 and veins of the leaves and petals, the slender 

 fibres of the stamens and pistils, and the firm and 

 woody fibres of the fruit. In the Lichens, Fuci, 

 and Fungi, no large tubes are discoverable even 

 with the aid of the microscope ; though in the 

 transverse section of most other plants they are 

 visible without a microscope. Such is the sub- 

 stance of M. MirbePs description of the large tubes 

 which he divides into the five following varieties : 

 simple tubes, porous tubes, spiral tubes, false spiral 

 tubes, and mixed tubes. 



The ARTICLE 1. Simple Tubes. The simple tubes 



large St f (Pi- VIII. Fig. 16.), which are the largest of all 

 the large tubes, are formed of a thin and entire 

 membrane, without any perceptible disruption of 

 continuity, and are found chiefly in the bark ; 

 though not confined to it, as they are to be met 

 with also both in the Alburnum and matured wood, 

 as well as in the fibres of herbaceous plants. But 

 they are particularly conspicuous in the stem and 

 other parts of the different species of Euphorbia 

 and Periploca ; and in all plants in general con- 

 taining thick and resinous juices, known by the 

 name of the proper juices, to the ready passage of 

 which their great width of diameter is well adapted. 

 Sometimes they are distinguishable by their colour, 

 4 



