CH. Il] TULIP. 29 



the power which the plant has of converting starch into 

 sugar. This power depends on the possession by the plant 

 of a ferment called diastase. 



The action of diastase will not be considered in detail 

 but it is worth noting that the essential features of the 

 process may be studied in any brewery. Barley is made 

 to germinate, its starch changes into sugar and is trans- 

 ferred to the sprout of the grain. Finally this sugar is 

 used by man with the help of another plant yeast to 

 make alcohol. 



Jerusalem Artichoke (Helianthus tuber osus). 



The Jerusalem Artichoke supplies an example of a 

 state of things similar to that described in the potato ; 

 the tuber is a swollen underground stem stored with 

 reserve-material 1 and bearing buds corresponding to the 

 eyes of the potato. They are relatively larger and more 

 obvious than those of the potato, and the leaves in whose 

 axils they grow are easily seen. 



Tulip (Tulipa gesneriana). 



When the flowering stem of the tulip appears above 

 the ground in the spring, it does so by means of growth 

 carried on by the expenditure of reserve material stored 

 up in the underground bulb ; so that from a physiological 

 point of view, the interest of the tulip-bulb is the same as 

 that of the tubers described above. Morphologically how- 

 ever it differs from these ; the chief bulk of the bulb is not 

 a solid mass like the potato, but is made up of fleshy scales 



1 The carbohydrate is not starch but inulin. 



