226 AGRICULTURE 



pondweed in some British lakes, and in the way 

 in which European weeds have monopolized 

 the pollution of Canadian fields. It is found 

 in the case of cereals that if seed be obtained 

 for a backward farm from a much earlier 

 district, the crop grown during the first 

 year or two ripens earlier, and furnishes a 

 " brighter " sample than the same variety 

 which has all along grown in the particular 

 district. 



Generally speaking, farmers import seed 

 from a dry climate to one that is moist, 

 and not vice versa ; and such practice appears 

 to be based upon sound physiological grounds. 

 A variety that has long grown in a district 

 of low rainfall, and with relatively dry air, 

 has adapted itself to make the most out of 

 such conditions. The cuticle, epidermis, and 

 stomata of its leaves have developed in such 

 a way as to retard expiration of water, with 

 the result that it can flourish luxuriantly 

 even when soil-moisture is not abundant, 

 or where the conditions encourage excessive 

 evaporation. These peculiarities are carried 

 in the embryos when the seed is transferred 

 to a new district, and even if the quantity 

 of moisture in the soil and air there be much 

 greater, the resultant plants seem capable 

 of rapid, adjustment to the new conditions, 



