ADAPTATION. 23 



Drought does not cause the vine to become more yellow. 

 The experiments we made on this are absolutely decisive. 

 Vines cultivated in pots were deprived during many weeks of 

 water; their leaves dried and fell off, but were not attacked 

 by chlorosis. Everybody has certainly had an opportunity 

 of seeing, at a certain time of the year, vines dry off after a 

 long drought. In 1890, 1891, and 1893 notably, vines in 

 many regions in France of the Charente, Bourgogne, and of 

 the shores of the Mediterranean and Rhone, etc., suffered 

 from drought so severely as to lose all their leaves, but 

 chlorosis was never noticed. Sometimes a very dry climate 

 may occasion chlorosis, which does not become manifest in a 

 cooler climate in soils of the same nature, as is, perhaps, the 

 case in the south of France (He'rault, etc.). This is due to 

 the drought forcing the roots to live deeper in a layer of cal- 

 careous sub-soil, but drought alone is not a cause of chlorosis. 

 It can only increase the evil, as in the case above mentioned; 

 more often it diminishes it. We will see later on in what 

 way. 



Drought and humidity acting alternately cannot be seriously 

 invoked, for quite frequently many plantations are submitted 

 to alternatives of drought and humidity, without, however, 

 suffering from chlorosis. 



According to this hypothesis, rains in certain soil would 

 drown the roots, which later on would become completely 

 dry. We have made researches to try and ascertain if this 

 hypothesis is correct. 



Vines cultivated for a long time in swamp land, saturated 

 with water, and suddenly exposed to an intense drought 

 never became yellow. In soils of Champagne, Charentes, 

 and Bourgogne, in patches of land where the vines wither, 

 in the Herault, Saint-Emillionnais, Blayais, etc., it does not 

 happen in those which become saturated with water and 

 subsequently become dry. Even after heavy rains those 

 soils may be worked, and in many of them vines have never 

 suffered from drought, and yet chlorosis obtains an intense 

 development. 



What is above described shows also that neither the 

 defective porosity of the soil nor excessive humidity can 

 cause the vine to turn yellow. 



Chlorosis and Iron. As previously stated, chlorosis is 

 characterized by the disappearance of chlorophyll from the 

 leaves and all herbaceous organs. Sachs has shown that 



