EFFECTS OF FOEEST YEGETATION Olf CLIMATE. 187 



the tv.'o last in the proportion to form water ; that the specific 

 gravity of the sap is least at the roots, and that (which may be 

 the cause of the hollowness of some of our Australian trees) it 

 ascends in the greatest quantity in the newest layers, and that 

 the innermost layers become clogged and hardened in the pro- 

 cess of assimilation, so that the vitality ceases there, and the 

 sap becomes deprived of the aqueous part of its constituents by 

 the deposition of ligneous matter. 



How water may be collected from invisible sources is a diffi- 

 culty for chemists and naturalists, which I do not venture to 

 solve. But, when we read of white ants, during a severe drought 

 in the heated parts of Africa, finding plenty of moisture beneath 

 the surface for making their plaster, though three inches deep 

 the thermometer stood at from 132° to 134° Fahrenheit — and of 

 other insects distilling (under experiment) from the castor oil 

 plant 16 ozs. of water in twenty-four hours, which are the state- 

 ments of Dr. Livingstone in his Missionary Travels (pp. 21 and 

 416, ed. of 1857), w^e must think that we know very little at 

 present of either vegetable or animal life. 



" We must," to use the great traveller's words, " leave it for 

 naturalists to explain how these little creatures distil both by 

 day and night as much water as they please, and are more 

 independent than Her Majesty's steamships with the apparatus 

 for condensing steam — for, without coal their abundant supplies 

 are without avail." 



It may be truly said that such phenomena as these can hardly 

 belong to the " effects of vegetation on climate " ; but in relation 

 to drought, which is very intimately connected with climate, it 

 may do no harm to show that there are alleviations of such a 

 calamity for some of God's creatures, which defy the wisdom of 

 man to parallel. We may thus be led to study the mysteries of 

 the visible creation with humility as to what we cannot dis- 

 cern, and with hopefulness as to what, by well-tempered zeal and 

 proper direction of what we may be permitted to discover, our 

 Sciences will finally attain. 



If, by a just employment of observation, we can arrive at any 

 positive means of counteracting the adverse, or employing the- 

 friendly forces of Nature to our advantage, it is not only per- 

 mitted us so to do, but it is our duty to do it, for the good of 

 mankind ; and it is not beneath the aim of rational and account- 

 able beings to seek guidance as to the planting of a wilderness or 

 the clearing of a jungle, if either be necessary, by inquiry as to 

 the facts which may be obtainable by experience, and accepted 

 as warnings or encouragements. 



There are some facts in relation to the ability of certain trees to 

 discharge water from their roots which will justify further refer- 

 ence to this branch of the subject, especially as the examples will be 

 selected from Australia, and have abcaring on its sanitarv conditions. 



