THE VEGETABLE CELL. 47 



originate together inside a cliloropliyll grannie ; for grannies of this kind 

 are met -with in subterraneous parts^in wliich no trace of cliloroph jU occurs, 

 as in tlie rLizome of Gloriosa superha. 



In many plants the starch is replaced by inuline, in many 

 parts, especially in the roots; e.g., in the tubers of the Dahlias, 

 of Helianthus annuus, &c. Since we possess no re-agent for it 

 this substance still escapes from microscopic investigation, even 

 if Schleiden's statement, that it occurs in the form of small gra- 

 nules, is well founded. Thus nothing is known respecting its 

 diffusion in the Vegetable Kingdom. 



Observ. According to Mulder's statement, inuline is coloured yellow 

 by iodine, this was the case with an inuline prepared from Taraxacmn 

 by Mulder, which I had an opportunity of examining. Other inuline, 

 which Prof Cbt\ Gmelin prepared for me from the Dahlia, was not colour- 

 ed in the least by iodine, even when I added tincture of iodine to the hot 

 solution, before the muJrne ^.as precipitated from it. 



d. Co7npoionds dissolved in tJie cell-sap. 



Certain compounds, most closely allied to starch and inuline, 

 escape j^om microscopic observation almost under all circum- 

 stances, notwithstanding their wide distribution in the Vegetable 

 Kingdom, because they are dissolved in the cell-sap, and there are 

 no means of detecting small quantities of them ; these are dextrine, 

 gum, and sugar. 



Dextrine seems to occur in all organs which are the seat of an 

 active process of nutrition, but can only be discovered in the ex- 

 pressed saps, not by microscopic observation. 



Other kinds of gum, gum arable, cherry-gum, tragacanth, the 

 mucilage of the seeds of Quinces, of Linseed, fee, playing a compara- 

 tively subordinate part, being diffused through but a small part 

 of the Vegetable Kingdom, are mostly to be considered as secre- 

 tion in the plants in which they do occur, and jfrequently are only 

 met with in isolated parenchymatous cells, as in Cactus, or in 

 the cells of particular organs, such as the seed-coats, or in cavities 

 and canals which lie between the cells, as in the Oycadese. When 

 such kinds of gum completely fill tbe cells or canals in which 

 they occur, they may be detected by the dense, sHmy mass which 

 they form with water, or by the coagulation caused by aicohoi ; 

 in manv cases, for instance in the cells of the seed-coat of Cydonia, 

 it is donUM Vhether tie gum is to be regarded as a sul-stance 

 secreted in the cavity of the cell or as forming secondary layers in 

 it. In any case the substance of which many cell-membranes 

 swelling up strongly in water are conmosed, such as the secondary 

 layers of the cells of the seed coat of Uollomia and of the pericarp 

 of Salvia, seems to be closely allied to these kinds of gum. So 

 long as these mucilaginous substances remain so loosely charac- 



