STRUCTURE OF THE FOLIAGE-LEAF 21 



the cells that compose it. Compare it with the 

 palisade layer. 



21. What fills the space between the mesophyll-cells? 

 Do these spaces connect with the outside air? 

 If so, how? 



THE VEINS 



22. At certain regions the section passes through veins, 

 presenting either cross, longitudinal, or other 

 sections of them. Note the greater differentiation 

 of the cells in the veins. This differentiation marks 

 the distinction between fundamental tissue or 

 parenchyma, and transformed tissue, prosenchyma. 

 There are several different kinds of prosenchyma. 



23. Using prepared slides, supplied by the instructor, 

 make a drawing of the cross-section of a leaf, show- 

 ing all features noted above. Make the drawing 

 at least 75 mm. long, and be careful to preserve the 

 natural proportions. 



24. The experiments on transpiration have shown that 

 living plants are constantly losing water. What 

 would be the result if no more were supplied? 

 What problem of plant life, therefore, naturally 

 arises? 



