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 of Acetabularia 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. 51, jE), a proof that 
the crystalline arrangement is 
not necessarily destroyed by 
the cell-walls. Similar forms 
(as in Fig. 51, 5) are formed 
when tissues containing inulin 
freeze ; and they do not again 
become dissolved in the cell- 
sap on thawing. Since the 
sphere - crystals consist of 
doubly refractive crystalline 
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 quan- 
tity of warm water of from 
5o°-55° C; 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- 
chloric acid the inulin is im- 
mediately transformed into 
glucose. Solutions of iodine 
in alcohol or water penetrate 
into 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 Compositae) 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 
may 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 in 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. R 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). 
