IRRIGATION. 231 



There is another view which is interesting, Viz. the manner in which domesticated anin^als 

 break up into groups : it ir illustrated in the dog, and all the domestic animals ; but those 

 groups retain the characte! istics of the species, and of all the changes which take place not one 

 afiFects the organization. The groups or varieties constitute well marked families, and are ca- 

 pable of preserving their identities as species. While species, as the dog and ox, possess a 

 constitutional ability to change their external characters, which are not specific, the change 

 itself is governed by a law which, while it marks the groups with characters transmissible to 

 their offspring, still not one group, or an individual of a group, is merged in any of the near or 

 remote species. I remark again, that specific character is never destroyed by external in- 

 fluences. In those instances where a species is changeable, and readily breaks up into groups 

 whose characteristics are transmissible from the parents to their offspring, the specific character 

 is never uprooted ; and in fact these external changes should be regarded as belonging to the 

 specific characters. It is true that this susceptibility can not be estimated or measured, as these 

 changes are regarded as accidents, or occurrences which can not be determined by law. 



IRRIGATION. 



There are two kinds of measures which may be put into a systematic operation, for effecting 

 a perfect irrigation. One is adapted to a field where there is a gentle slope, with a stream 

 passing in a favorable direction, from which there may be sent numerous little branches, which 

 may be turned upon it, and which may inosculate with each other and meander over the pas- 

 tures or meadows. A gentle current is required, which should be directed through the en- 

 closure in the least expensive manner, and the channel should never pass through hollows or 

 depressions where the water will stand and accumulate. Means should also be devised for 

 governing and controlling the water during excessive rains and freshets. A careful inspection 

 of the ground is required, in order to secure all the advantages of fertilization of which this 

 mode of applying water is susceptible. Another form of irrigation consists in flooding a piece 

 of meadow-land at favorable pe.*iods, and over which the water may stand for a short period, 

 and deposit the earthy matters which may be suspended in it. Nature in this case must favor 

 the desired object. A stream must be dammed at the proper place, or at that point where its 

 flow may be controlled. The water, on being elevated by the dan», will be made to flow in 

 shallow channels, which also may lead into one main channel. With the proper arrange- 

 ment the surface of the meadow may be laid under water, and let off at will. This project 

 may be put in operation eithe.r in the spring or autumn, when the crops are not on the 

 ground. The object in this form of irrigation is to supply, at a small cost, the fertilizers sus- 

 pended in the water. The most favorable time for doing this is when the streams are swollen 

 and turbid. The fertilizers, in this case, belong mainly to the mineral kingdom, and are du- 

 rable though not active. This form of irrigation requires a careful survey of the ground, and 

 a judicious system of channels and gates to control the flow of water. If the water is let upon 

 the grounds during the growth of the crop care should be taken to avoid the deposites of the 



