The Cultivation of Watercress. 



827 



to running waters ; it must, however, not be confused with the 

 wild type, which has much larger leaves, and is inferior in 

 quality, and less. prolific. The Green variety is usually asso- 

 ciated with still waters, wherein the use of manures stimulates 

 its growth and increases its yield for cutting. Cases of 

 typhoid have, however, been traced to this particular variety 

 when grown in polluted water, a danger which never occurs 

 with the Brown-leaved variety. 



Source of Water Supply. — The majority of districts in 

 which watercress is now grown are favoured with a supply of 



Watercress Bed before Cutting. 



pure fresh water from springs, usually having their origin in 

 the chalk formation. The temperature of these springs does 

 not generally vary much from 50 0 F., and extremes of heat 

 and cold are thus guarded against. Some waters, having a 

 higher temperature, and probably containing different mineral 

 ingredients from others, are favourable to the production of 

 early crops. The further the beds are from the source of the 

 spring, the less productive they become, as the plants suffer 

 from the variation of temperature, which gives the older 

 foliage a yellow and sickly appearance. On the other hand, 

 water having too high a temperature encourages the produc- 

 tion of puny and discoloured plants. 



3 G 2 



