56 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS 



In ordpr to ascertain the relations of the parts, and to get 

 their names, consult Principles, Fig. 112. l^our section is by no 

 means exactly like the figure ; sketch it. Label properly all the 

 parts shown in your sketch. 



Are any differences noticeable between the upper and the lower 

 epidermis ? Between the layers of cells immediately adjacent to 

 each ? Test some sections with phloroglucin (Sec. 12, D). 



B. Examine with a power of 200 or more diameters the outer 

 surface of a piece of epidermis from the lower side of the 



• leaf.^ Sketch carefully, comparing your sketch with Prin- 

 ciples, Fig. 113, and labeling it to agree with that figure. 



C. Examine another piece from the upper surface ; sketch it. 

 How does the number of stomata in the two cases compare ? 



E-EFEREXCE. Strasburger-Hillhouse, 6. 



43. Study of the leaf of " rubber plant " (Ficus elastica)* * 



A. Make preparations of the leaf of the so-called rubber plant 



as already described for the lily leaf. Study and sketch them 



and then compare the two types of leaf : 



1. As regards thickness of epidermis. 



2. As regards number of layers of cells in the epidermis. 



3. As regards development of the palisade layers. 



4. As regards amount of fibro-vascular material (veins). 



5. As regards freedom of exposure of the stomata openings 

 to the air. 



ivy (Heclera), willow, maple, poplar (any species, as cottonwood, aspen, etc.), the 

 thicker-leaved species of aster, apple, pear, plum, quince, beet. Thin sections 

 may be cut free-hand, especially if the leaf is doubled together several times or 

 held between two bits of elder pith. If only a part of the section is very thin, it 

 will answer almost as well as if it were equally thin throughout. The sections 

 may be made much more transparent if they are soaked in potash solution until 

 most of the green color disappears, and then treated with acetic acid. Both 

 these sections and those in their natural condition should be examined. Some 

 sections in their natural condition should be treated with phloroglucin. 



1 The epidermis may be started with a sharp scalpel and then peeled off with 

 small forceps and movinted in water for microscopical examination. The epidermis 

 of Ficus leaf (Sec. 43) will need to be pared off with a very sharp razor held par- 

 allel to the leaf surface. The stomata may be counted by use of an eyepiece 

 micrometer ruled in squares. Find how many divisions of the stage micrometer 

 equal one side of this square; then substitute a bit of epidermis for the stage 

 micrometer, and count the number of stomata in an eyepiece square. Calculate 

 the number of stomata in a leaf of the kind examined; also, if possible, the 

 number for the entire plant. 



