C PREFACE. 



with few exceptions tlie varieties that have orig'inated in arid regions, 

 Avhere the soils are usually more saline than in humid regions, are 

 those that are most resistant to pure solutions of sodium and magne- 

 sium salts. Three varieties of southeastern Eussia, with one excep- 

 tion, were found to be the most resistant of all those tested. 

 ' It is believed that the laboratory work upon which this paper is 

 based has a direct practical bearing, as it gives us an indication of 

 what A'arieties are most likely to succeed in arid regions where the 

 soils are more or less salty. Furthermore, as some one salt — e. g., 

 sodium chlorid — sometimes strongly predominates in the soils of a 

 particular region, and as these experiments show clearly that, while 

 one variety may be more resistant than another to sodium chlorid. 

 the second is often more resistant than the first to sodium carbonate 

 or to magnesium sulphate, we can thus obtain information as to 

 which of the many varieties of a great crop can be sown with the 

 best chance of success upon a given type of alkali soil. In other 

 words, a few weeks of simi)le lal)oratory experiment may save years 

 of costly trial in the field, although, of course, the water-culture exper- 

 iments can not be considered as giving more than an indication of 

 what we can expect each variety to do. and the final test must be the 

 growing of the crop upon a practical scale. 



The great individual variability in resistance brought oiit in these 

 experiments shows that not merely have we found a guide as to which 

 of existing varieties are best adapted to diiferent types of saline 

 soils, but that there is an excellent opportunity for increasing their 

 resistance by selecting seed from the most resistant individuals. 

 The present investigation alfords further evidence that it is practi- 

 cable to apply plant-breeding methods to the " alkali problem "' and 

 adapt crops bj^^ selection to the unfavorable conditions presented by 

 soils that contain excessive amounts of soluble salts. 



A. F. AVooDS, 

 Patholof/ist and Physiologist. 



OFriCE OF Vegetable Pathological 



AMD PlIYSIOLO<;i(AL INVESTIGATIONS, 



Washington, D. 6'., April 26, 1005. 



