The best evidence that the humus is alive is the fact that it breathes. The fungi which are destitute of chlorophyll absorb oxygen and give off carbonic acid, in this respect resembling animals and differing from the chlorophyll-bearing plants. The most easily obtained evidence of this is the fact that decaying refuse generates heat, a fact which is easily ascertained by using a thermometer. Thus I have at present in the garden of my cottage in the Thames Valley a heap of privet leaves intermixed with a quantity of fine twigs which give it great porosity and serve to admit a large quantity of air. On the morning of October 21 the temperature of the air was 39° F., and the temperature of the heap of leaves was 57° (18° more than the air). On October 22 there was a heavy cold rain with a cold easterly wind. On the morning of October 23 the temperature of the air was 40° and the temperature of the heap of leaves was 56°. On the night of October 23-24 there was (for the time of year) a very severe frost. My heap of leaves on the morning of the 24th was solidified on the surface by the frost, but the temperature of the interior was 53° while that of the air was 30° (an increase of 23° over the air). This heap, it should be stated, is only a small heap, and would all go into a big wheelbarrow. On the morning of October 24, after taking the temperature of this heap, I turned it over with a fork, putting the frozen top in the centre and altering the position of the constituents of the heap. A quarter of an hour later the temperature of the heap was found to be 32°, and at seven in the evening it was still at freezing-point, or only just above it. The night of October 24-25 was again very frosty, as many as 12° of frost having been registered at a house close by. At eight in the morning of the 25th, however, my heap of leaves showed a temperature of 40°, having risen 8° during this very cold night, and being 20° above the minimum cold recorded in the night. At 7 P.M. on the 25th the temperature of the heap was 42°, and the next morning, after a third very cold and frosty night, it had risen to 45°. The rise of temperature here was clearly due to the respiration of living things, and could not have been in any degree caused by absorption of sun heat. (Since the above was written autumn has come upon us, and the fallen leaves have been collected into a big heap. On November 15 the temperature of this heap was found to be 62° F., and a week later (November 22) had risen to 104° F.!) The fact that the humification of organic matter generates heat is a fact which is of enormous practical value to the gardener and farmer. The market gardens round London, which produce astounding crops and assimilate an enormous quantity of dung, are in a sense extended and mild hotbeds. One hopes that those who are advocating the burning of organic refuse will pause to think, however necessary such a process may be under certain circumstances,