THE CELL- SAP. 



63 



obtained by pressure or boiling, it precipitates spontaneously after some time in the form 

 of a white fine-grained precipitate. From solutions it crystallises in the form of so- 

 called Sphere-crystals (Fig. 51 A), consisting of crystalline elements disposed in a radiate 

 manner. Within the cells it may be made visible as a finely granular precipitate by 

 drying or by rapid removal of water by alcohol (Fig. 51, F). It is abundantly pre- 

 cipitated in the cells on dipping thin sections of the tissue into alcohol, in the form of 

 smaller sphere-crystals which become readily visible on addition of water (Fig. 51, B). 

 They are obtained much larger by laying entire specimens oi Acetahularia or large pieces 

 of tissue containing inulin (tubers and stems of the dahlia or Jerusalem artichoke) for 

 a longer time in alcohol or 

 glycerin; in the latter case a 

 sphere-crystal very commonly 

 includes several cells of the 

 tissue (Fig. 5 1, £), a proof that 

 the crystalline arrangement is 

 not necessarily destroyed by 



fthe cell-walls. Similar forms 



[(as in Fig. 51, JS) are formed 

 ^hen tissues containing inulin 



[freeze ; and they do not again 



[become dissolved in the cell- 



[sap on thawing. Since the 



^sphere - crystals consist of 



f doubly refractive crystalline 



i elements arranged radially, 



'they show, with polarised 



[light, the characteristic cross. 



|They are not' capable of 

 swelling, are slowly dissolved 

 in a large quantity of cold 



[water, rapidly in a small qu an- 

 ility of warm water of from- 



■ 5o°-55° G. ; in nitric or hydro- 



[chloric acid or potash solu- 

 tion they dissolve easily, the 

 solution always commencing 

 from without; by boiling in 

 very dilute sulphuric or hydro- 



|<;hloric acid the inulin is im- 



Imediately transformed into 



Iglucose. Solutions of iodine 



[in alcohol or water penetrate 



finto the fine crevices of the 



[sphere-crystals, but produce 



'no special colour. Inulin-structures are easily and certainly recognised by these re- 

 actions. If masses of tissue containing much inulin (tubers of Inula Helenium and 

 Jerusalem artichoke, roots of dandelion and of other Gompositae) are examined in the 

 air-dried state, the parenchymatous cells are found to be filled with angular, irregular, 

 shining, colourless fragments, which are seen in polarised light to be crystalline, and 



:inay be recognised as inulin by the reactions above-named. 



If the ovaries and unripe fruits of the orange or citron are laid for some time in 



alcohol, concretions are found m their tissues, which completely resemble in form the 



sphere-crystals of inulin ; but the chemical reactions and the degree of solubility show 



[that they do not consist of this substance. Pfeffer has examined these structures more 



Fig. 51. — Sphere-crystals of inulin. A from an aqueous solution laid 

 aside for 21 months ; at a the action of nitric acid is commencing. B cells of 

 the root-tuber of the dahlia ; a thin section was placed for 24 hours in alcohol 

 of 90 p. c, and was then dipped in water. C two cells with half sphere-crystals 

 having their common centre in the middle of the separating cell-wall ; from an 

 internode 8 mm. thick at the apex of an older plant of the Jerusalem artichoke 

 which had remained for some time in alcohol. D fragment of a sphere-crystal. 

 E a large sphere-crystal including several cells, from a larger piece of the 

 stem-tuber of the artichoke, after lying for a longer time in alcohol. F inulin 

 after evaporation of the water from a thin section from the same {X 500; E 

 not so much). 



