SPECIFIC STABILITY. 129 



acid, forms hexagonal tabular prisms ; but if a little am- 

 monia is added, the form changes to that of a long rectan- 

 gular prism, with secondary planes in the angles. If a 

 little more ammonia is added, several varieties of rhombic 

 octahedra appear ; if a little nitric acid is added, the 

 rectangular prism appears again. The changes take place 

 not by the addition of new crystals, but by changing the 

 growth of the original ones." These, however, may be 

 said to be the same species, after all ; but recent researches 

 by Dr. H. Charlton-Bastian seem to show that modifications 

 in the conditions may result in the evolution of forms so 

 diverse as to constitute different organic species. 



Mr. Murphy observes r 1 "It is scarcely possible to doubt 

 that the various forms of fungi which are characteristic of 

 particular situations are not really distinct species, but that 

 the same germ will develop into different forms, according 

 to* the soil on which it falls." It is possible, however, to 

 interpret the facts differently, and it may be that these are 

 the manifestations of really different and distinct species, 

 developed according to the different and distinct circum- 

 stances in which each is placed. Mr. Murphy quotes Dr. 

 Carpenter 2 to the effect that "NoPuccinia but the Puccinia 

 rosce is found upon rose bushes, and this is seen nowhere 

 else ; Omygena exigua is said to be never seen but on the 

 laoof of a dead horse ; and Isaria felina has only been 

 observed upon the dung of cats, deposited in humid and 

 obscure situations." He adds, " We can scarcely believe 

 that the air is full of the germs of distinct species of fungi, 

 of which one never vegetates until it falls on the hoof of a 

 dead horse, and another until it falls on cat's dung in a 



1 "Habit and Intelligence," vol. i. p. 202. 

 "Comparative Physiology," p. 214, note. 

 K 



