22 AMERICAN VINES. 



(6) Cause of Chlorosis. The opinions advanced to explain 

 the yellowing of the vine, and the distortment often result- 

 ing from it, are numerous. 



Chlorosis has been attributed to humidity, to drought, or 

 to alternatives of drought and humidity, to the climate, to 

 lack of iron in the soil, to deficient coloration, and, therefore, 

 heating power of the soil, to grafting, to ' ' special properties, ' ' 

 to carbonate of lime, etc. 



Chlorosis and Humidity. We have previously shown that 

 excessive humidity of the soil has a certain influence on the 

 growth of the vine. Can it bring about chlorosis? It 

 sufnces to examine vines planted in very damp soils, but 

 non-calcareous, to satisfy oneself that it is not due to 

 humidity. In the Chatentes, in Cognac, in Holland, where 

 vineyards are under water during the winter and part of the 

 spring, so much so that culture is impossible up to the 

 month of June, vines never become yellow, and if sometimes 

 patches of chlorosis become manifest, it is always on the top 

 of small calcareous rises, which, however, are drained well, 

 although without being excessively dry. It is the same in 

 the Saumurois, where the vines planted on the cretaceous 

 banks of the Loire, which are aways dry, are frequently 

 yellow, while those planted on the plain, which is very damp, 

 never become yellow. In Bourgogne the vines on the hills 

 become yellow in certain places every year; the vineyards 

 on the plain established in siliceous clay soil, compact, and 

 retaining water, are always completely green. In the 

 Gironde and in Languedoc such examples are common. 



Vines planted on the banks of rivers, in old swamp 

 badly drained (such as certain vineyards established on the 

 Marine Sands in the Charente-Inferieure (Arvert, etc.), in the 

 Bouches-du-Rhone, the Loire-Inferieure, where the water is 

 oft^en 12 to 1 6 inches over the surface, never show signs of 

 chlorosis. 



One of us, during a whole year, cultivated Riparias in ordi- 

 nary water; they bore branches 24 inches long, and a 

 small number of short roots, without developing the slightest 

 patch of yellow on the leaves. An excess of humidity alone 

 has, therefore, no action on the yellowing of the vines. As, 

 however, in certain soils (calcareous), it is in spring, and after 

 very frequent rains, that vines become most yellow, no doubt 

 water has a certain action. We will study this case later 

 on. 



