TISSUE. 



95 



side of the leaf of Anemone nemorosa, for example, there 

 are none ; on the lower side there are 43,215 to the square 

 inch ; on the leaves of Indian Corn 

 there are on every square inch on 

 the upper side 60,630, and on the 

 lower side 101,910 stomates ; on the 

 Sycamore leaf there are none on the 

 upper side, but on the lower side 

 179,310 to the square inch. In the 

 leaf of the common Sunflower there 

 are in each square inch : above, 

 112,875 ; below, 209,625. Through 

 the stomates, or breathing pores, an 

 interchange of gases takes place. 

 121. Thefibro-vaseular bundles are 

 composed of tracheary tissue, sieve-tubes, and parenchyma. 

 They may be easily separated from the other tissue in the 

 petioles of the Plantain, in the stems of Indian Corn, etc. 

 When examined in section, they are seen to consist of two 

 parts, namely, wood, called xylem ; and bast, called 

 phloem (Fig. 213). When cambium (delicate cells, rich 

 in protoplasm, capable of division) is present between tliem, 

 the bundle is said to be open (Fig. 214, a diagram) ; if it 

 is absent, it is said to be a closed bundle (Fig. 215, a dia- 

 gram). Open bundles continue to 

 increase in size, new layers of 

 wood and new layers of bast being 

 formed from the cambium. The 

 bundles, which are isolated when 

 the plantlet is very young, increase 



214 



215 



Fig. 213. Transverse section of a fibro-vascular bundle ; P/t, phloem ; JCy, xylem; 

 C, cambium. Figs. 214, 215. Diagrams illustrating open (1/4) and closed (31^ bun- 

 dles. 



