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IOWA ACADEMY OF SCIENCES. 



connected. Midway between the large bundles are small ones 

 (Fig. 12), connected with the epidermis by a narrow, wedge- 



st. 



Fig. 12. 

 Cross section of keel, lower side, showing .secondary bundle with its parts, sur- 

 rounded by mesophyll, c. p. s., chlorophyll parenchyma sheath; p. phloem; at. stere- 

 aome; par. colorless parenchyma. (Orii^inal.) 



shaped area of stereome, and almost surrounded by a thick- 

 walled chlorophyll parenchyma sheath, and this sheath by 

 another thin- walled one which might be called the mesophyll 

 sheath. 



Midway between each large and small bundle is usually a 

 smaller one, isolated, and entirely surrounded by a double 

 sheath, one of thick-walled chlorophyll parenchyma, and the 

 second of thin-walled mesophyll. These are true mestome 

 bundles, like those of the blade proper. 



The area not occupied by stereome, between the outer epi- 

 dermis and the bundles, is occupied by chlorophyll parenchyma 

 or mestome. 



