240 



THE SECOND BOOK OF BOTANY. 



FIG. 407. 



Are there also differences in the parenchyma of 

 the upper and under sides of leaves ? Make a verti- 

 cal section of the blade of any fresh, ordinary leaf, 

 and observe the structure. Compare it with Fig. 

 407. Are not the cells much more closely packed 

 on the upper than on the under 

 side ? In the figure you see the 

 upper side, composed of three 

 rows of closely - packed cells, 

 placed end to end, while in the 

 lower half the cells are placed ir- 

 regularly, and the tissue is full of 

 intercellular spaces. You see in 

 this portion of the section the cut- 

 ends of vessels and fibres, where 

 a vein has been severed. This 

 is but one out of many different 

 modes of arrangement ; but, in 

 all such leaves as turn one side 

 toward the sky and the other toward the ground, 

 there will be found more or less difference in the 

 structure of the upper and under portions. 



Remove a bit of the epidermis, or skin, of a leaf, put 

 it upon the glass, with a drop of water, and examine 

 it with the microscope. Is there any chlorophyll in 

 its cells? How are the cells arranged? Is there 

 more than one layer ? Does your specimen exhibit 

 any such appearances as are seen among the cells in 

 Fig. 408? Examine a fresh bit of skin from the 

 under surface of a leaf, and you will surely find 

 them. They are much larger and more numerous in 

 some leaves than in others. Between and under- 

 neath these two oblong cells there is an opening 



