176 THE CARBOHYDRATES 



These colour reactions are indicative of the formation of 

 sugar by the hydrolysis of the inulin by the acids employed 

 in the tests ; it is therefore important, before employing these 

 reactions, to make sure that no free sugars are present in the 

 material to be examined, and to wash the preparations 

 thoroughly with alcohol in order to remove them. 



Since inulin does not reduce Fehling's solution, this re- 

 agent may be employed to ascertain whether any reducing 

 sugars are present in the material before employing the above 

 tests for inulin. 



The following reactions may be carried out with a solution 

 of inulin. 



3. Basic lead acetate gives no precipitate with inulin. 



4. Inulin is precipitated from solution by alcohol. 



5. Hydrolyse with mineral acid and test for levulose. 



Physiological Significance. 



It is of interest to find that the nature of the reserve carbo- 

 hydrates may often be correlated to the habitat of the plant. 

 Parkin * points out that these reserve substances of aquatic 

 plants and of plants inhabiting wet situations take the form 

 of starch, e.g. Sparganium, Alisma, Listera, Orchis, and Schizo- 

 stylis ; whereas, on the other hand, inulin, generally associated 

 with sugar, is the characteristic carbohydrate reserve in those 

 Monocotyledons inhabiting dry situations, e.g. Allium, Aspho- 

 delus, Anthericum, Yucca, Tritona, Iris Xiphium, etc. 



In this connection f reference must be made to the work of 

 Lidforss, who showed that plants inhabiting wet situations 

 fall into two distinct categories ; those like Elodea, Chara, and 

 Stratiotes, which hibernate at the bottom of the pond or stream, 

 contain starch but no sugar ; while those which live on the 

 banks where their rhizomes, or other organs of storage, pass 

 the winter out of the water, e.g. Myosotis and Menyanthes, 

 contain sugar during the winter months. In the former case 

 a temperature of —2° C. to —4° C. is fatal, while in the latter 

 case the death point is about —7° C. 



* Parkin : " Phil. Trans. Roy. Soc, Lond.," B, 1899. 191, 169. 

 t See Blackman : " New Phyt.," 1909. 8, 354. 



