Manganese in Land and Fresh Water Mollitsca. 71 



amounts in the soil, 1 and its relative absence in the higher 

 animals is in correspondence with their superior selective 

 power. It seems, however, that snails must necessarily take 

 it up in their food, whatever sort of vegetable or animal that 

 may be, and in a certain number of cases it accumulates in 

 them. They do not, on the whole, appear to show any pre- 

 ference for manganiferous food ; potatoes, containing very 

 small traces, are eaten readily enough, Arion hortensis and 

 H. rujescens will climb high into trees to eat apples 2 ; L. stag- 

 nates will swarm on to a cabbage leaf or a dead frog) while the 

 plants around them contain far more manganese. But I ad- 

 mit that the difference between, e.g., Bnliminus and Helicelloi 

 may turn out to be due, partly at any rate, to a preference by 

 the former for a cryptogamic diet, though on any diet they 

 would probably maintain their relative positions in the manga- 

 nese scale. 3 Experimental feeding is the obvious solution ; 

 but the basal diet would have to be white of egg, with perhaps 

 a little potato and mammalian muscle, and even this would 

 not be quite innocent of manganese. 



I have not been able to find any extensive series of analyses 

 giving the quantity of manganese actually present in different 

 plants, and such analyses might be misleading if, as is prob- 

 able, the quantity varies much in different localities. 4 A few 

 analyses have been made of local vegetation 5 which gave the 

 following results (parts manganese per ten thousand of plant 

 dried at ioo° C.) : — 



1 cf. ;he general occurrence of titanium in plants, C. E. Wait, /. 

 Amcr. Chcm. Soc, 1896, p. 402 ; and in mammals, C. Baskerville, ib. Vol. 

 XXI., 1S99, p. 1099. 



2 E. A. W. Peacock, The Naturalist, 1902, p. 139. 



3 Testacella has less than most slugs ; earthworms from my garden 

 gave 0-9 per ten thousand. Hyalinia are of course not exclusively, and 

 perhaps only occasionally, carnivorous. 



4 F. Jadin and A. Anstruc (Compte's Revdvs, Vol. CLV. (1912), p. 406) 

 in more than So species in 32 families found frcm 0-014 to 7-6, with a 

 variation from o-i to 2*0 in different lots of mistletce. 



5 The currant tea and tobacco both gave 1*9 parts. 



1917 Feb: 1. 



