RECENT SCIENCE. 633 



culminating point in the yellow, and descends toward both ends 

 of the spectrum ; it exactly corresponds with the curve of assimi- 

 lation of carbon by plants under variously colored light. It is 

 also remarkable that the green color of the pupa is only obtained 

 by yellow light, or by such green as contains yellow ; such is, as 

 known, the average color of leaves. We thus have a case where en- 

 vironment itself makes the color which approximately matches it. 

 The meaning of these researches is self-evident. No naturalist 

 will probably attempt to explain the animal colors and markings 

 without the aid of natural selection. But it becomes less and less 

 probable to admit that the animal colors are a result of a selection 

 of accidental variations only. The food of the organism, and 

 especially the amount of salt in it, the dryness or moisture of the 

 air, the amount of sunshine, and so on, undoubtedly exercise a 

 direct effect on the color of the skin, on the fur, and on the very 

 intimate anatomical structure of the animal. As to the relative 

 parts which must be attributed in the origin of each separate 

 variation to natural selection on the one side, and to the direct 

 action of environment on the other side, it would simply be un- 

 scientific to trench upon such questions in a broadcast way, so 

 long as we are only making our first steps in discriminating the 

 action of the latter agency. The first steps already indicate how 

 complicated such questions are, especially in those cases where 

 natural selection must act in an indirect way — not as a mere 

 selection of already modeled forms, but as a selection of forms 

 best capable to respond to the requirements of new conditions — 

 in which case the intimate organization of the living being comes 

 in the first place. All we may say at the present moment is that 

 the direct modifying action of environment is very great, and 

 that no theory can claim to be scientific unless it takes it into 

 consideration to its full amount. — Nineteenth Century. 



Mb. W. Roe, of the Cape Colony, has pointed out a disadvantage connected 

 with irrigation. Most water used for the purpose contains variable quantities of 

 soluble salts, some of which are not taken up largely by plants. Every applica- 

 tion of water, therefore, adds to the saline ingredients of the soil — a very differ- 

 ent effect from that of excess of rain water, which, so far as there is open subsoil 

 for it to drain away, would be likely to take out rather than add to the soluble 

 salines in the soil. The mischief of the accumulation of salts in the soil is aggra- 

 vated in a dry-air land where evaporation is great. The air, acting like a sponge 

 on a surface, takes up the water, leaving the accumulated salts in the surface soil. 

 But this surface soil is as the sponge to the layer beneath. Constantly after each 

 water-leading, the water is drawn to the surface and evaporated, leaving the ac- 

 cumulated salts in the surface soil. The harm done by this accumulated salt will 

 depend on the nature and quantity of the salines in the water used, as also upon 

 the quantity of water supplied. 

 vol. xliii. — 46 



