366 THE BIOLOGY OF THE PLANT 



Mtcroscopic Characters. 



Make cross and longitudinal sections of the 

 various petioles, and compare them with one an- 

 other and with sections of the stem. At least 

 three cross - sections of each petiole should be 

 made — the first at the base, the second near the 

 middle, and the third near the apex. Note the 

 tissues present, their arrangement, and the distri- 

 bution of the fibro-vascular bundles. Study sur- 

 face sections showing the epidermis. 



Examine both surfaces of each leaf with the 

 low power, noting the areas into which the small 

 veins divide the soft tissues and the distribution 

 of stomata. Make sections and study the struct- 

 ure of each leaf, noticing especially the arrange- 

 ment and structure of the epidermal cells, of the 

 green tissue or mesophyll — some of whose cells 

 form the palisade parenchyma, next the epi- 

 dermis — the contents of the various cells, and the 

 arrangement and structure of the fibro-vascular 

 bundles. 



Make the drawings necessary to show the facts 

 observed. 



How many and which leaves show decided 

 structural differences between the upper and 

 lower surfaces? "What are these differences in 

 each case ? "What reasons can you give for the 

 arrangement and contents of the palisade cells? 

 Compare the structure of leaves with that of the 

 fern frond examined, and with the thallus of 

 Marchantia. 



