386 ORCHIDE^. 



especially if of large size. The ovoid tubers are from 1 to 1| 

 inches in length, and, if of good quality^ have a creamy white 

 colour, or are somewhat translucent and of a horny texture. 

 They have hardly any odour and an insipid mucilaginous taste. 

 The tubers should be plump and not wrinkled. When magni- 

 fied, the bulk of the tuber is seen to consist of a parenchyme, 

 the cells of which contain either mucilage, or starch altered by 

 heat ; it is traversed by small fibre- vascular bundles. 



Chemical composition, — The most important constituent of 

 salej) is a sort of mucilage, the proportion of which, according to 

 Dragendorff (1865), amounts to 48 per cent. ; but it is, doubtless, 

 subject to great variation. Salep yields this mucilage to cold 

 water^ forming a solution which is turned blue by iodine, and 

 mixes clearly with neutral acetate of lead like gum arabic. On - 

 addition of ammonia, an abundant precipitate is formed. Muci- 

 lage of salep j)^^ecii)itated by alcohol and then dried, is coloured 

 violet or blue, if moistened with a solution of iodine in iodide 

 of potassium. The dry mucilage is readily soluble in ammo- 

 niacal solution of oxide of copper ; when boiled with nitric acid, 

 oxalic, but not mucic, acid is produced. In these two respects, 

 the mucilage of salep agrees with cellulose, rather than with 

 gum arabic. In the large cells in which it is contained, it does 

 not exhibit any stratification, so that its formation does not 

 appear due to a metamorphosis of the cell-wall itself. Mucilage 

 of salep contains some nitrogen and inorganic matter, of which it 

 is with difficulty deprived by repeated precipitation by alcohol. 



It is to the mucilage just described that salep chiefly owes 



it 



thick 



which becomes still thicker on addition of magnesia or borax. 

 The starch, however, assists in the formation of this jelly ; yet 

 its amount is very small, or even nil in the tuber bearing the 

 flowering stem, whereas the young lateral tuber abounds iu it. 

 The starch so deposited is evidently consumed in the subsequent 

 period of vegetation, thus explaining the fact that tubers are 

 found the decoction of which is not rendered blue by iodine, 

 Sulep contains also sugar and albumin, and, when fresh, a trace 

 of volatile oil. Dried at 110^ C, it yields 2 per cent, of ash. 



