2G4 SCIENCE IN SHORT CHAPTERS. 



trees grow, and thus continually return to it all they have taken 

 away. 



They do something besides this. During the winter they grad- 

 ually decay. This decay is a process of slow combustion, giving out 

 just as much heat as though all the leaves were gathered together and 

 used as fuel for a bonfire ; but the heat in the course of natural 

 decay is gradually given out just when and where it is wanted, r,nd 

 the coating of leaves, moreover, forms a protecting winter jacket to 

 the soil. 



I am aware that the plea for this sweeping-up of leaves is the de- 

 mand for tidiness ; that people with thin shoes might wet their feet 

 if they walked through a stratum of fallen leaves. The reply to this 

 is, that all reasonable demands of this class would be satisfied by 

 clearing the foot-paths, from which nobody should deviate in ihe 

 winter time. Before the season for strolling in the grass returns, 

 Nature will have disposed of the fallen leaves. A partial remedy 

 may be applied by burning the leaves, then carefully distributing 

 their ashes ; but this is after all a clumsy imitation cf the natural 

 slow combustion above described, and is wasteful of the ammoniacal 

 gaits as well as of the heat. The avenues of Bushey Park are not 

 going so rapidly as the old sylvan glories of Kensington Gardens, 

 though the same robbery of the soil is practised in both places. I 

 have a theory of my own in explanation of the difference, viz. that 

 the cloud of dust that may be seen blowing from the roadway as the 

 vehicles drive along the Chestnut Avenue of Bushey Park, settles 

 down on one side or the other and supplies material which to some 

 extent, but not sufficiently, compensates for the leaf-robbery. 



The First Commissioner speaks of efforts being made to restore 

 life to the distinguished trees that are dying. Let us hope that these 

 include a restoration to the soil of those particular salts that have for 

 some years past been annually carted away from it in the form of 

 dead leaves, and that this is being done not only around the " distin- 

 guished " trees, but throughout the gardens. 



Any competent analytical chemist may supply Mr. Adam with a 

 statement of what are "these particular salts. This information is 

 obtainable by simply burning an average sample of the leaves and 

 analyzing their ashes. 



While on this subject I may add a few words on another that is 

 closely connected with it. In some parts of the parks gardeners may 

 be seen more or less energetically occupied in pushing and pulling 

 effective mowing-machines, and carrying away the grass which is 

 thus cut. This produces the justly admired result of a beautiful 

 velvet lawn ; but unless the continuous exhaustion of the soil is 

 compensated, a few years of such cropping will starve it. This sub- 

 ject is now so well -understood by all educated gardeners, that it 

 should be impossible to suppose it to be overlooked in our parks, as 

 it is so frequently in domestic gardening. Many a lawn that a few 

 years ago was the pride of its owner is now becoming as bald as the 

 head of the faithful, " practical," and obstinate old gardener who so 

 heartily despises the " fads" of scientific theorists. 



When natural mowing-machines are used, i.e. cattle and sheep, 

 their droppings restore all that they take away from the soil, minus 

 the salts contained in their own flesh, or the milk that may be 

 removed. An interesting problem has been for some time past 



