244 MANUAL OF MODERN VITICULTURE. 



system was entirely different from that of the Rupestris St. 

 George. Very few of the main roots went down to the 

 moist regions of the soil ; most of the main roots were 

 superficial, growing about 1 foot below the surface, and 

 sending out small rootlets. The roots were not strong, but 

 rather brittle, and broke easily ; 32 cuttings out of 40 were 

 well rooted, that is 80 per cent. 



Solonis. 45 cuttings were planted in the spring, and 

 were treated like the preceding. The following observations 

 were made on the vines when taken out in the winter : The 

 shoots were thin and of an average length of 2 feet. The 

 roots were well developed and grew down to the moist 

 depths, although not so straight as the roots of the Rupestris 

 St. George. The small rootlets and root hairs were only 

 formed at the end of roots 3 to 4 feet deep in the soil. The 

 main roots were thicker than those of Rupestris St. George 

 and Riparia Gloire de Montpellier. 



The difference in character of the root systems of Rupes- 

 tris, Riparia, and Solonis is well shown by Fig. 183. These 

 are average specimens of the vines rooted at the St. 

 Helena plot in 1899. The tendency of the Riparia to send 

 out horizontal or even slightly rising roots is illustrated. 

 In extreme cases the roots were found to start toward the 

 surface at an angle of about 45, and after rising in this way 

 for several inches to become horizontal. About two-thirds 

 of the roots took this horizontal direction, and the remainder 

 went down at various angles, some being nearly vertical. 



The cause of the failure of the Riparia in the upper part 

 of the Napa Valley is evidently to be found here. The heat 

 and continual drought of summer penetrates to these hori- 

 zontal roots, destroy the root hairs, and deprive the vine of 

 water exactly at the time it is most needed. The more deeply 

 penetrating roots are too weak, and too few to supply the 

 amount of water needed by the evaporating leaf surface. 

 This lack of adjustment of the supply of water to the demand 

 is increased when the Riparia is grafted with strong growing 

 Vinifera varieties. This is evidenced by the many grafted 

 vines which die in their second or third year. 



The deeply-penetrating roots of the Rupestris shown in 

 th e figure explain the resistance of this species to drought. 

 All the roots of this young vine penetrated deeply into the 

 soil in a direction more or less approaching the vertical. As 



