60 STUDY OF COMMON PLANTS. 



2. A layer or two of closely packed cells, with their 



long diameter perpendicular to the surface of the 

 leaf, containing many chlorophyll bodies. These 

 constitute the palisade tissue. 



3. Other chlorophyll-bearing cells essentially the same as 



the preceding, but less regular in shape and more 

 loosely arranged, so that toward the lower surface 

 of the leaf large openings, intercellular passages, 

 occur. Some of these cells contain large stellate 

 crystals of oxalate of lime. 



4. About midway between the upper and lower surface, 



the veins, fibre-vascular bundles, cut either trans- 

 versely or at an angle, according to their direction 

 at the place where the section is made. The 

 thick-walled mechanical elements constitute the 

 bundle-sheath. The bundle itself is divided into 

 two adjacent parts, the xylem lying towards the 

 upper surface of the leaf, and the phloem towards 

 its lower surface. The tracheids of the xylem, 

 elongated tube-like structures, are easily recog- 

 nized. 



5. The lower epidermis, similar to the upper, but with 



stomata at frequent intervals. These are placed 

 so that each one forms an entrance to one of the 

 intercellular passages. (Sections of the stomata 

 are best studied in a hyacinth leaf.) 



NOTE. The different sections should be studied until the gen- 

 eral structure of the leaf is thoroughly understood. Every fact is 

 of physiological significance, and it is of the utmost importance 

 that the student should have a complete and clear knowledge of 

 the minute anatomy based on direct observation. 



