THE LEAF 227 
transpires about 180 gallons of water per day and that during a 
growing season of five months it would give off water enough to 
cover the ground shaded by it to the depth of 20 feet. 
Types oF Leaves DEVELOPED IN ANGIOSPERMS.—These may 
be tabulated as follows: 
1. Cotyledons (the primitive or seed leaves). 
2. Scale leaves. 
3. Foliage leaves. 
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ay Th JATT ®) eo 
iY, ‘ , 
ras rt, 
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Fic. 156.—Semi-diagrammatic cross section of a DorstvENTRAL Lear of a meso- 
phyte showing by arrows how the water passes from the tracheal elements of 
a vein into the border parenchyma cells, and thence into the palisade and spongy 
parenchyma, from which it evaporates into the intercellular spaces and passes 
from the leaf through the stomata. a, upper epidermis; 4, lower epidermis; ¢, 
palisade parenchyma; g, spongy parenchyma; d, border parenchyma; e, tracheal 
elements; and the stippled cells below ¢, the phloem cells. (After Stevens.) 
4. Bract leaves; (a2) primary at base of inflorescence; (5) 
bracteolar leaves (bracteoles) at the base of individual flowers. 
5. Sepals. 
6. Petals. 
7. Microsporophylls (stamens). 
8. Megasporophylls (carpels). 
CotyLepons.—Cotyledons are the first leaves to appear upon 
the ascending axis and are single in Monocotyledons, double in 
Dicotyledons. Occasionally, as in certain Maples, there may 
be three cotyledons shown. This is due to a splitting of one of 
the cotyledons. There exist no true cases of polycotyledony 
(development of many cotyledons) among Angiosperms, as in 
