FUNCTION.] OF TISSUE. 167 



is converted into starch, carbonic acid being evolved (granting 

 that starch is the only substance upon which iodine acts so 

 characteristically) . 



"4. The third (1. c.) by boiling in caustic potash is con- 

 verted into a peculiar, as yet unknown (?), vegetable prin- 

 ciple, which is coloured orange yellow by iodine. Whether 

 in this case carbonic acid be also formed, I will not take 

 upon myself to decide ; at least in Experiment VIII., on the 

 addition of sulphuric acid, I did not observe any efferves- 

 cence. Moreover, this orange colour is as distant as heaven 

 from earth, from the colour produced by adding iodine to 

 vegetable mucus. 



" Whether the carbonic acid be formed at the expense of 

 the carbon of the vegetable substance uniting with the 

 oxygen of the air, or by the decomposition of the water, 

 remains still to be investigated; as, likewise, to discover 

 whether by longer boiling, it could take up more carbon, and 

 become converted into oxalic acid. 



"The most interesting result is, however, without doubt, 

 that, by the action of the caustic potash, one portion of vege- 

 table matter becomes, by a retrograde metamorphosis, as it 

 were, again converted into starch ; a discovery, the extension 

 of which gives promise of most interesting results for organic 

 chemistry." 



In another place Schleiden gives the following general 

 summary of the chemical condition of vegetable substances : 

 " The vegetable substances, usually called indifferent, and 

 which belong to the starch series, form but a small part of 

 the infinitely varied materials which occur in plants. Plants 

 form during their vegetation an elementary chemical matter 

 (no allusion is here meant to the old notions of primitive 

 mucus), which has the same elementary composition in all 

 stages of vegetation ; but is capable of infinite modifications, 

 owing to imperceptible internal changes, and especially to 

 the increase and diminution of the water in combination 

 with it. These modifications depend, however, not merely 

 on the number of atoms of water but also on the combina- 

 tions of different elements, and at present seem to form a 

 continuous series, the contiguous members of which do not 



