132 IEEIGATION. 



cumstances favor it ; (such as a location upon a stream 

 where there is sufficient fall, to avoid heavy embanking, 

 which however is a rare occurrence) ; but when the slope 

 exceeds that ratio another system must be adopted. Be- 

 sides the systems of water meadows, previously described, 

 there are other methods of irrigating grass lands which 

 will be explained hereafter. 



The time of continuance and intervals of irrigation of 

 these meadows is of importance. There is always danger 

 that, by reason of a rise of temperature, vegetation may 

 be unduly stimulated. In such a case the water, only in- 

 sufficiently charged with oxygen, cannot supply the de- 

 mands of the plants, and they are destroyed unless the 

 water is withdrawn and air supplied, or the temperature 

 lowered by exposure until the stimulus is removed. An 

 interval of a few days is then to be given before the water 

 is again turned on. An irrigation of 10 or 15 days and 

 an interval of five is the general practice. Whenever 

 practicable, a meadow may be divided into three or four 

 portions in the manner before described. Then, in the 

 first case, by flooding two of the divisions, and at the end 

 of five days drawing ofi* the water from the first and turn- 

 ing it upon the third, and after five days more drying the 

 second and flooding the first, and so on continuing, each 

 division would be ten days under water and five days dry. 

 In the second case, if three are under water in succession 

 and one dry, each will be 15 days irrrigated and dry for 

 five days. It is impossible to give directions in each case; 

 the experience of the operator must be his guide, and the 

 beginner must exercise caution, learn to know when he is 

 right, and then go ahead. A reference to the principles 

 upon which irrigation depends for its good effects, and 

 the circumstances which would make it injurious, must 

 be carefully made whenever there is doubt in the mind of 

 the operator. The general rule already stated, that it is 

 much more common, and easy, to err upon the side of 



