THE CELL-SAP. 



63 



material, are, as such, not immediately the subject of morphological observation, to 

 which we are for the time confining ourselves. Inuline ^ only, which is precipitated by 

 the action of cold and desiccating agents from its solution in cell-sap in definite forms, 

 and becomes visible in the interior of cells, need here be particularly mentioned. In the 

 cell-sap of certain Algae (Acetabularia) and many Compositae (perhaps also in many 

 other plants), Inuline, a substance closely related to starch and sugar, occurs. In sap 

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

 form of a white fine-grained pre- 

 cipitate. From solutions it cry- 

 stallises in the form of so-called 

 sphere-crystals (Fig. 53, A), which 

 consist of crystalline elements 

 disposed in a radiate manner. 

 Within the cells it may be made 

 visible as a finely granular preci- 

 pitate by drying or by rapid re- 

 moval of water by means of al- 

 cohol (Fig. 53, F). It is abun- 

 dantly precipitated in the cells in 

 the form of smaller sphere-crys- 

 tals on dipping thin sections of 

 the tissue in alcohol, becoming 

 immediately visible on addition of 

 water (Fig. 53, B). They are ob- 

 tained much larger by laying whole 

 Acetabularias or large pieces of 

 tissues containing inuline (tubers 

 and stems of Dahlia and Helianthus 

 tuberosus) for a longer time in al- 

 cohol or glycerine ; in the latter 

 case a sphere-crystal very com- 

 monly includes several cells of 

 the tissue (Fig, 53, E), a proof 

 that the crystalline arrangement 

 is not necessarily destroyed by 

 the cell-walls. Similar forms (as 

 in Fig. 53, B) are formed when 

 tissues containing inuline freeze, 

 and they do not again become dis- 

 solved in the cell-sap on thawing. 

 Since the sphere-crystals consist 

 of doubly refractive crystalline 

 elements arranged radially, they show, under polarised light, the cross which occurs under 

 such circumstances. They are not capable of swelling, are slowly dissolved in a large 

 quantity of cold water, and quickly in a small quantity of warm water of from 50^-55° 

 C. ; in solution of potash and nitric and hydrochloric acids they dissolve easily, the solu- 

 tion always commencing from without ; by boiling in very dilute sulphuric or hydrochloric 

 acid the inuline is immediately transform.ed into glucose. Solutions of iodine in alcohol 

 or water penetrate into the fine crevices of the sphere-crystals, but occasion no special 

 colour. Inuline-structures are easily and certainly recognised by these reactions, as 



Fig. S3.— Sphere-crystals of Inuline. A from an aqueous solution laid aside 

 for 2i months ; at a the action of nitric acid is commencing. B cells of the 

 root-tuber of Z)<7/j//« Wrtr/a^i'to; a thin section was placed for 24 hours in alcohol 

 of 90 p.c, and was then dipped m 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 Helianthus titberosiis, 

 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 

 tuber of Heiiauthus tuberosus, after lying for a longer time in alcohol. F 

 Inuline after evaporation of the water from a thin section from the tuber of 

 Helianthtis tuberosus (X500; E not so nmch). 



^ Sachs, Bot. Zeitg. p. 77, 1864.— Prantl, Das Inulin, ein Beitrag zur Pflanzen-Physiologie. 

 Preisschrift. Munich 1870.— Diagendoiff, MateriaUen zu einer Monographic des Inulins. Petersburg 

 1870. 



