in regard to Earthy Matters. 17^3 



taken to cut off a supply. Hence the inference would seem to 

 be, that the indications of a contrary description that sometimes 

 present themselves are fallacious, resulting from the many im- 

 perceptible channels by which earthy and alkaline matter may 

 obtain admission to the juices of a plant*. Had I not very 

 early in the course of these experiments been led to despair of 

 excluding the minute but continual supplies, which are probably 

 brought by the very air and water which come into contact with 

 the absorbing surfaces of every vegetable, especially in the cen- 

 tre of a large town, I.should not have remained satisfied without 

 purifying the sulphate of strontian in which the seeds were sown 

 from the other earths with which I found it to be mixed. But 

 the labour of getting rid of these ingredients seemed to be un- 

 called for with reference to the objects to which I found it ne- 

 cessary to confine my inquiries; since, even had I employed the 

 earth in a state of perfect purity, and detected an excess of lime 

 in the plants reared in it beyond that contained in their seeds, 

 still I should not have been justified in inferring the actual ge- 

 neration of earthy matter, any more than I have felt myself to 

 be from the similar result I obtained when flowers of sulphur 

 were the matrix in which the plants had vegetated. The fa- 

 culty, however, possessed by them of rejecting strontian, even 

 when presented to the absorbing surfaces of their roots in a state 

 of solution, would seem sufficiently substantiated ; and an ana- 

 logous circumstance may be cited in the animal kingdom, if I 

 can rely upon an experiment which I made several years ago, 

 that of confining some hens of the Guinea-fowl during the breed- 

 ing season in a place where they could obtain no other earth, 

 except some powdered sulphate of strontian, which they appear- 

 ed to devour greedily. Yet only a minute trace of this earth 

 was discoverable in the shells of their eggs, of which those laid 

 during the first part of their confinement retained their natural 

 hardness, but those of later production were as soft as if the 



* The case which I should be most disposed to bring forwards in support of 

 the contrary opinion is that of the phosphoric acid, which forms so abundant 

 an ingredient in all animal structures. Is its quantity sufficiently accounted 

 for by that introduced into the system by the food taken in ? On this sub- 

 ject I hope at some future time to complete some experiment?. See also Dr 

 Prout's paper on the phosphate of lime existing in the young chick before the 

 egg is hatched. 



