54 



The following rule is given by L. Fortes and F. Ruyssen, and will 

 be found to hold good in the majority of cases, although some 

 American sorts are very similar to a Vitis Vinifera, and vice versd. 

 Fig. 7 represents a typical leaf of Vitis Vinifera, and Fig. 8 one of 

 Vitis Labrusca (an American species), which may to some extent 

 serve as a type for them all.* 



FIG. 7. 



FIG. 8. 



The most characteristic difference between the two and the only 

 one presenting any degree of fixity is in the petiolar sinus or main 

 indentation, where the petiole or leaf stalk joins the limb or flat part 

 of the leaf. In the Vitis Vinifera the edges, after separating at 

 first, tend to join again higher up, giving the opening the form of a 

 U which has been closed in at the top ; in the Vitis Labrusca, on 

 the other hand, it is more similar to a V which has been widened 

 above so that the extremities point outward. The portion of the 

 leaf above the insertion of the petiole is far more considerable in the 

 Vitis Vinifera than in the Vitis Labrusca, or the insertion of the 

 petiole is much nearer the centre of the leaf in the former 

 variety. The texture of the leaves presents a somewhat charac- 

 teristic difference. Those of the American sorts appear to be more 

 or less flabby, whilst the leaves of Vitis Vinifera have a more crisp 

 appearance. 



* It must be borne in mind that the general form of the leaf is not always 

 as in the cuts; for example, V. Vinifera frequently has three-lobed and V. 

 Labrusca five-lobed leaves. The two examples given are the most common forms 

 of each species. 



