REACTIONS OF INULINE. 



69 



sity for cutting longitudinal sections to show the striate structure. 

 It is a widely- spread phenomenon that the cross walls in a tissue 

 are thickened differently to the longitudinal walls a phenomenon 

 probably associated with the differing demands on their perme- 

 ability for the conduction of food-materials, etc. 



Inuline. If the section is laid in absolute alcohol there arises 

 in the cell-sap a fine precipitate of Inuline. Replace the alcohol 

 by water, and warm the object-slide over a spirit flame, and the 

 precipitate is again dissolved. In order to study the inuline in 

 the shape of sphsero-crystals, it is best to examine pieces of 

 tubers which have been placed in about 50 per cent, alcohol at 

 least eight days before. We examine the section best in water, 

 and during the examination allow nitric acid very slowly to enter. 

 The sphsero -crystals or sphaerites (Fig. 25) are always found on 

 the cell-walls, forming more or 

 less perfect balls. The ball can 

 be traversed by cell- walls. Usu- 

 ally several variously sized balls 

 form together a larger group. 

 The balls allow a radial structure 

 to be more or less clearly recog- 

 nised ; this structure comes out 

 more sharply when the nitric acid 

 begins to work ; it arises from 

 radially arranged needle-shaped 

 (acicular) crystals, which com- 

 pose the ball. In the growing 

 sphgerite they are deposited in 

 concentric layers, whence arises 

 its concentric lamination. Iodine 

 solution produces no coloration. 

 If the sphaero - crystals are 



warmed in a drop of water on 



, , . ,., ,, . , , 



the Object-slide they quickly 



dissolve. For the 



of inuline in solution in the 



tissues an alcoholic solution of orcin can be used. If sections are 



saturated with this, and then boiled in hydrochloric acid, a deep 



orange-red colour is produced if inuline be present. Any sphae- 



rites of inuline which may be present are, of course, dissolved in 



the process. Phloroglucin can be used instead of orcin, with a 



recognition mon ^ ) s j 



FIG. 25. From the tuber of Dahlia 

 i*, after lying in spirits for many 

 Sphsero-crystals on the walls 



