6 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



re-establishing vineyards on resistant stock. Happily, in California we 

 do not have to contend with that part of the problem, as few soils con- 

 tain enough lime to affect even the Riparias and Rupestris, that are 

 among the first to suffer from excess of carbonate of lime. 



The compactness of the soil, generally due to the large proportion of 

 clay it contains, is an obstacle to the good growth of many varieties of 

 resistant stock; the roots do not penetrate easily, the ground is cold 

 and often wet, and under such conditions the Rupestris and Riparia, 

 for instance, do poorly. On the contrary, the Lenoir, Champini, 

 Riparia X Rupestris No. 3306 and 101 14 will do well in such locations, 

 and the hybrids of Solonis X Cordifolia X Rupestris will do still better. 

 The last-mentioned have a higher resistance to phylloxera than Lenoir 

 and Champini. If we examine the probable cause for the special 

 adaptation to heavy soils, we see that whereas the Riparia and Rupes- 

 tris have light, thin, hard roots very much ramified; on the contrary 

 the varieties adapted to such soils have strong, fleshy roots, less 

 ramified, with a heavier hair system on the rootlets. 



When in excess, the moisture in the soil affects the vine by checking 

 the growth of the root system. Plants growing in a very moist place 

 may have a vigorous aerial growth, but the root system is generally 

 weak; such a plant will suffer greatly if for some reason the supply of 

 moisture should fall below the average. The root system in a dry 

 exposure will always be much more vigorous, as the plant has to send 

 its roots lower down to find the water it needs. On the other hand, a 

 moist soil will help a vine in its fight against phylloxera, and under 

 such conditions some stocks, though inferior in absolute resistance, may 

 do fairly well. As a general rule, the Solonis and its hybrids are very 

 good in wet soils. 



The fertility of the soil is a condition of adaptation that we must not 

 overlook: A Riparia or a Solonis will turn yellow and look sick in a soil 

 where a Rupestris would do fairly well. This does not mean that a 

 Rupestris will not do better in a good soil than in a poor one, but simply 

 that it is more rustic in its adaptation. 



VARIETIES OF RESISTANT STOCK. 



We give below the adaptation of the principal varieties of resistant 

 vines used as grafting stock or as parents in the making of hybrids. 

 (Riparia, Rupestris, Candicans, Cordifolia, Monticola, Arizonica, Cali- 

 fornica, Berlandieri.) 



Vitis riparia. The V. riparia (see title-page) is very resistant to 

 phylloxera (18).* The grafts made on this stock are fructiferous, 

 vigorous, and advanced in maturity. All varieties root readily from 



*Resistance to the phylloxera is indicated by figures on the scale of 20 points. 



