29 



form on their surface, the carbonic acid being extracted from 

 the plant and combining with the lime. All the cases in 

 which it may still be doubtful whether the solitary crystals 

 are surrounded with a cellular membrane or not, have been 

 fully treated of; but it would occupy too large a space in this 

 limited report, were I to enumerate the new facts from the 

 memoirs published by me during the past year. I shall there- 

 fore only touch on my own labours of that period when the 

 facts therein contained stand in contradiction to the observa- 

 tions of others. 



In M. Unger's observations on the frequency of crystals in 

 plants, he remarks, that it is not strictly determined whether 

 the age and locality of the plant contribute essentially to this, 

 although it may certainly be admitted. I think, however, that 

 physiology is at present pretty clear as to this point ; for we 

 know, that plants absorb all that the soil offers them in a 

 dissolved state, that the quantities of the various substances 

 which are absorbed bear an exact proportion to the degree of 

 solution in which these exist, and also to the quantity of the 

 solution which passes through the plants. The solid sub- 

 stances remain in the plants, for the water is evaporated ; and 

 then the various acids produced in the plants, as also those 

 which are imbibed, can carry on the process of their affinity. 

 The age of the plant, the age and vital condition of the single 

 parts, the transpiration which is different at the various parts, 

 and the degree of solubility of the substances to be crystallized, 

 are all circumstances which explain the manifold occurrence 

 of crystals in vegetables. In the cells containing oxalic acid, 

 oxalate of lime will be formed. No amylum can have ex- 

 isted if the oxalic acid was contained in the cell previous to 

 the existence of the lime, for this is converted by the slow 

 action of acids into sugar, &c. And thus might we explain the 

 remarkable phenomenon mentioned by M. Unger (1. c. p. 5.) : 

 " Amylum, green-coloured cellular sap globules, coloured cel- 

 lular sap, cells with crystals, &c., all these occur frequently in 

 single but neighbouring cells, and in the cells themselves we 

 do not see the reason of these various formations. " 



M. Unger notices the difficulties which are opposed to the 

 observation of the crystalline forms, but has figured the va- 

 rious forms of the crystals contained in several plants, for in- 



