{5} Gardeners Chronicle, April 17, 1869, p. 418.
{6} Mr. Darwin s attention was called by Professor Hensen to P. E.
Muller s work on Humus in Tidsskrift for Skovbrug, Band iii. Heft 1 and
2, Copenhagen, 1878. He had, however, no opportunity of consulting
Muller s work. Dr. Muller published a second paper in 1884 in the same
periodical a Danish journal of forestry. His results have also been
published in German, in a volume entitled Studien uber die naturlichen
Humusformen, unter deren Einwirkung auf Vegetation und Boden, 8vo.,
Berlin, 1887.
{8a} Bidrag till Skandinaviens Oligoch tfauna, 1871.
{8b} Die bis jetzt bekannten Arten aus der Familie der Regenwurmer,
1845.
{9b} There is even some reason to believe that pressure is actually
favourable to the growth of grasses, for Professor Buckman, who made many
observations on their growth in the experimental gardens of the Royal
Agricultural College, remarks ( Gardeners Chronicle, 1854, p. 619):
Another circumstance in the cultivation of grasses in the separate form
or small patches, is the impossibility of rolling or treading them
firmly, without which no pasture can continue good.
{11} I shall have occasion often to refer to M. Perrier s admirable
memoir, Organisation des Lombriciens terrestres in Archives de Zoolog.
exper. tom. iii. 1874, p. 372. C. F. Morren ( De Lumbrici terrestris
Hist. Nat. 1829, p. 14) found that worms endured immersion for fifteen
to twenty days in summer, but that in winter they died when thus treated.
{12} Morren, De Lumbrici terrestris Hist. Nat. &c., 1829, p. 67.
{14} De Lumbrici terrestris Hist. Nat. &c., p. 14.
{17} Histolog. Untersuchungen uber die Regenwurmer. Zeitschrift fur
wissenschaft. Zoologie, B. xix., 1869, p. 611.
{18a} For instance, Mr. Bridgman and Mr. Newman ( The Zoologist, vol.
vii. 1849, p. 2576), and some friends who observed worms for me.
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