LEAVES 



145 



FIG. 58. Net 

 veining. 



Method. Examine the leaves selected, giving special 

 attention to the under surface where the veins are more 

 prominent. The network is easily discovered 

 in most' leaves, but in cases of some leaves it 

 will be necessary to hold them between the 

 eye and the light. Fleshy leaves often do 

 not show their net veining because there is so 

 much pulp in them. Tear a leaf as in the 

 preceding Experiment and note how irregu- 

 larly it tears. Why? Study the general 

 plan of the veins and discover if possible the 

 general scheme of veining. 



Conclusion. How many types of net- 

 veined leaves can you find? 



Note. The veining of leaves usually indicates the kind of plant, 

 whether monocotyl or dicotyl. 



Parallel veining is never found in dicotyl plants, and net veining 

 very rarely in monocotyl plants. 



Such monocotyls as arrowhead (sagittaria), elephant's-ear 

 (caladium), and a few others seem to have net venation, but a close 

 examination will show that the veins run generally parallel with each 

 other and only the large ribs form a sort of network. 



Leaf Impressions 



For greater ease in studying leaves, the use of leaf impres- 

 sions is very helpful. They may be made in the following 

 manner : 



Apply a preparation of vaseline and lampblack to the under 

 surface of the leaf, using a dabber made of tightly rolled 

 cotton batting covered with chamois skin. 



The leaf should be touched lightly all over its under sur- 

 face, and great care should be used not to have much of the 

 preparation on the dabber. 

 EXP. BOT. 10 



