lo April, 191 i.] Rain Trees. 235 



-drops, and as a general rule, is deposited more readily upon inanimate 

 •objects than upon living plants. 



In the case of certain desert plants which become covered with saline 

 incrustations, it has been suggested that these incrustations may aid in 

 drawing moisture from the air, and so providing the plant with water. 

 As a matter of fact, the presence of such incrustations on the leaf would 

 tend rather to draw water out of the leaf than from the air, if they had 

 any appreciable effect at all, and so instead of providing the plant with 

 water, would probably aid in robbing it of what it had. 



Trees and plants generally do not directly affect the rainfall of a 

 country to any appreciable extent, although the presence of timber on land 

 has the same effect as an increase in the rainfall, and that in various ways. 

 Firstly, the shelter afforded by belts of timber protects the land between 

 from scorching winds. Secondly, the soil is held up and kept loose and 

 jjermeable to a greater depth on forest country than on the hard, open, 

 baked soils of plains. Hence, less of the rain runs off, more penetrates 

 and to a greater depth, from which it is steadily drawn bv the trees dur- 

 ing the dry months. This is a very important factor in keeping the ain 

 moist and also in moderating the temperature within a \ery limited, but 

 still quite appreciable range. 



In regard to the so-called "Rain Tree" of Peru, this is highly re- 

 commended by Baron von Mueller as a rapidly growing shade tree, par- 

 ticularly for roadsides. He also mentions that the foliage is shut up at 

 night so that rain and dew fall through and thus allow grass lo grow 

 beneath. The foliage, however, also closes up more or less in strong sun- 

 light, so that it is difficult to see how the tree can be classed as a good 

 shade tree, and it is in fact largely the absence of complete shade which 

 allows grass to grow beneath it. The statement is al.so made on the 

 authority of the Consul for France at Laroto, that its foliage possesses 

 the power to an unusual extent to attract and absorb aerial humiditv. So 

 far as is known, no tree has any such special power. A dense stretch of 

 tall timber, by compelling rain clouds to pass over at a slightly higher 

 elevation, may aid in .squeezing out a little tnore moisture than if the trees 

 were not there, but this is a purely physical action strictly comparably 

 with the action of a mountain range in causing rain to fall from the clouds 

 as they ascend to pass over it and hence lose heat. The action can never 

 be very pronounced, since the densest belt of timber is not nearly so per- 

 fect a barrier as a mass of land of equal height, and an average difference 

 of thirty to a hundred feet or so in elevation is, under ordinary circum- 

 stances, only a small factor in influencing rainfall. 



This particular tree, under the name of " Rain Tree," has been largelv 

 exploited and .sold in Australia, under the erroneous supposition that it 

 •could be credited with special rain-making properties. As has already 

 been mentioned, it has no special influence upon the rainfall, and its action 

 in ameli(jrating climatic conditions in bare treeless localities, does not differ 

 from that of any ordinary freely growing tree. So that the use of the 

 term " Rain Tree" for this plant, in the sense mentioned above, is ab.so- 

 lutely incorrect. The name probal)ly arises from the fact that, during 

 dark rain-storms, the leaflets fold together in the same way that they do in 

 darkness, .so that the tree gives no shelter from the rain, and the use of 

 the name in its later significance is only another instance of how the mean- 

 ings of names are corrupted or distorted, especially when doing .so enables 

 the .set^d of only a moderately useful tree to be .sold at a price and in 

 quantities l)ey<ind its real value. 



