PHYSIOLOGICAL BOTANY. 241 



Chemie/ 32, Bd. s. 198. He subjected Cetraria Islandica 

 and Ayaricus albus to elementary analysis, and his results 

 agree tolerably well with those of Pay en. He then makes 

 the following remark : " I am also satisfied as to the 

 perfect accuracy of his experiments, yet I cannot deny that 

 I am astonished, first, at not finding it stated* anywhere 

 that he previously determined the amount of ash, except 

 in his first memoir (Annal. des Sciences Natur., 2 ser. 

 t. ii, p. 27), since even if he had not found any ash pre- 

 sent, he ought to have mentioned it; moreover, since 

 none of the substances mentioned by myself as having 

 been analysed were perfectly free from the so-called in- 

 crusting matter, and since the results of Payen lead to 

 the same conclusion, which is explained by the intimacy 

 with which these substances permeate the primary cellular 

 tissue ; and again, since silica, which is so generally dif- 

 fused throughout the vegetable kingdom, would very 

 probably have entered into the composition of these 

 matters, it does not appear possible that the vegetable 

 structures subjected to examination could have been per- 

 fectly free from silica." This suggestion is quite correct. 

 Payen gives the amount of ash contained in the vegetable 

 structures when not yet separated from the matters depo- 

 sited upon the cellulose. We thus find that 10*80 p. c. of 

 silica are stated to exist in the leaves of Endive, but none 

 in the leaves of the same plant when exhausted of every- 

 thing but the cellulose. This is very improbable, for the 

 amount of silica in the leaves of the Graminaceas, before 

 purification, is stated to be 12'25 ; but I find no analysis 

 given of the leaves after purification. But in this case 

 the amount of silica existing in the cellulose must be very 

 large, for the incinerated leaf is so completely converted 

 into silica, that all its parts can be accurately distinguished 

 under the microscope ; a remarkable phenomenon, and 

 one which still requires careful investigation, because it 

 is opposed to what we know regarding cellulose. 



In the same ' Scheikundige Onderzoekingen/ 1. c. p. 62, 

 ' Journal f. Prakt. Chemie,' 1. c. pu 204, we have an 



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