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BOTANY OF CROP PLANTS 



Key to Important Genera 



The three most important genera are Vitis (grape), Cissus (pepper 

 vine) and Parthenocissus (Virginia Creeper and American Ivy;. These may 

 be distinguished as follows (as far as our species are concerned) : 

 Leaves simple or pinnately compound. 



Petals united into a cap, falling away without separat- 

 ing (Fig. 210), Vitis (grape). 

 Petals separate, spreading, Cissus (pepper vine). 

 Leaves digitately compound, Parthenocissus (Virginia 

 creeper, American ivy). 



VITIS (Grape) 



Stems. — Grapes are climbing or woody 

 vines with tendrils. The stem is jointed. 

 The internodes have a large pith. In many 

 species there is a woody tissue (diaphragm) 

 at the nodes separating the pith; in others 

 this woody tissue is absent (Fig. 207). In 

 pruning the vines, the practice is to make 

 the cut through the nodes rather than through 

 the internodes; by cutting through an inter- 

 node, the pith shrinks, leaving a hollow in 

 which water may collect and rotting set in. 

 Grapes have a tendency to produce suckers 

 and water sprouts. The former arise from 

 below or near the surface of the ground and 

 should be removed. Water sprouts arise 

 from dormant buds above ground. They do 

 not produce fruit. If dormant buds de- 

 velop, producing these sterile shoots, it in- 

 dicates that there is not a sufficient number 

 of fruit buds to take care of all the sap 

 coming to aerial parts. Water sprouts should 

 be removed during winter pruning. 



Tendrils, morphologically, are modified stems. This is 



Fig. 207. — Two 

 types of grape 

 stems cut in me- 

 dian lengthwise 

 section. A, south- 

 ern fox grape 

 (Vitis rotundifo- 

 lia) with pith con- 

 tinuous at the 

 nodes; B, old 

 world grape (V. 

 vinif era) with pith 

 interrupted at the 

 nodes. (After 

 Hedrick.) 



