23(5 CONTRIBUTIONS TO 



the substances which differ in a chemical sense; and just as 

 little do I require that chemists should approve all my terms 

 and characteristics (independent of this, perfection at the pre- 

 sent time would be an impracticable task) ; I shall merely 

 notice in a few words the most important modification s, their 

 consequence and signification in the course of the develop- 

 ment of vegetable organization, in order to avoid repetitions 

 in future. 



In the plant starch appears almost to take the place of 

 animal fat. It is superfluous nutritive material, which is de- 

 posited for future use; and we therefore usually find it in 

 places where a new formative process is to commence after a 

 short repose, or where a too luxuriant life has generated a 

 superabundance of nutritive material. It has of late been the 

 subject of such deep research that it is unnecessary for me to 

 enter upon it more fully ; I will merely refer the reader to 

 the most recent and practical summary of the results in 

 Meyen's Physiologie, Bd. I, p. 190, &c. 



The starch is sometimes supplanted by a semi-granulous 

 substance ; for instance, in pollen, the albumen of some plants, 

 and frequently in the cells of the leaf, as matrix of the 

 chlorophylle. It is chiefly distinguished by its occurrence in 

 irregular, granulous forms, which have no internal structure, 

 and from its being coloured a brownish -yellow or brown by 

 tincture of iodine. This substance, which I shall call mucus, 

 is probably identical with that of which the cytoblasts are com- 

 posed, and with the small granules in gum, which I shall pre- 

 sently mention. Meyen has already remarked the probability 

 of the first supposition (Physiologie, Bd. I, p. 208). 



But when the starch is to be employed in new formations, 

 it becomes dissolved, in a manner as yet quite unknown in 

 chemistry, into sugar or gum, the latter sometimes appearing to 

 pass into the former, or vice versa. The sugar appears in the 

 form of a perfectly transparent fluid, which is almost as clear 

 as water, is not rendered turbid by alcohol, and receives from 

 tincture of iodine only so much colour as corresponds to the 

 strength or weakness of the solution of the reagent. 



The gum appears as a somewhat yellowish, more consistent, 

 and less transparent fluid, which is coagulated into granules by 

 tincture of iodine, assuming a pale yellow permanent colour. 



