70 



ELEMENTS OF GENERAL SCIENCE 



toward the tip of the blade ; smaller veins branch out from 

 this and extend obliquely toward the edge. These smaller 

 veins branch again and again, until the smallest of them are 

 invisible to the naked eye and form a very fine and close net- 

 work. This is the pinnate (feather-like) type of veining. Other 



leaves, like those of 

 the geranium or 

 nasturtium, have no 

 single central vein, 

 but instead several 

 large veins extend 

 outward like a fan 

 from the end of 

 the petiole. These 

 leaves have the 

 palmate (hand-like) 

 type of veining. 

 There are other 

 leaves, like that of 

 the common plan- 

 tain, in which the 

 principal veins all 

 start from the peti- 

 ole and run nearly 

 parallel toward the 

 tip of the blade. 

 There is no con- 



A, parallel-veined leaf of the lady's-slipper orchid ; , 



B, pinnately veined leaf of the elm ; C, palmately S P 1( BtWOrK. 

 veined leaf of the maple ; D, palmately veined leaf The grasses also 



of the water shield .,, . , . , . n 



illustrate this kind 



of veining. These leaves are said to be parallel-veined. 



The spaces between the veins in the meshes of the network 

 are filled with a soft, green material called the mesophyll. This 

 material is very easily injured by contact with anything and 

 quickly dries if exposed to air. It is protected by a thin skin, 



FIG. 38. Examples of leaves 



