116 THE NUTRITIVE FUNCTIONS. 



though sometimes crystallized as an excretion in the nec- 

 t-aries of flowers, yet in the plant exists only in the fluid 

 state. It is found very abundantly in growing parts, such 

 as buds, germinating cotyledons, and in ripening fruits. 



When starch passes from the solid to the fluid state it is 

 converted into gum and sugar. This transformation is 

 effected by means of a vegetable secretion termed diastase 

 elaborated for this purpose, and which may be readily ob- 

 tained in a separate state from the neighborhood of the 

 eyes or buds of the potato. The starch thus rendered 

 fluid is called dextrine, which is conveyed to all those 

 parts of the plant where growth is going on. In flowering, 

 the starch in the receptacle of the flower is converted into 

 sugar, as nutritive material for the development of the 

 pollen granides of the anthers and the young ovules of the 

 germen; whilst that portion of this sugar which is not 

 required, again assumes the form of starch in the cotyle- 

 dons of the seeds, to be once more reconverted into sugar 

 for the nourishment of the young germ, as soon as its vital 

 activity again commences. The saccharine matter is ela- 

 borated by organs called nectaries, developed for this pur- 

 pose. This sweet juice is changed to honey in the stomach 

 of the bee. It is the food of the bee, which is furnished 

 with collecting organs for the purpose of removing it from 

 the plant. 



Volatile and fixed oils. — The volatile or essential oils 

 are met with in the stem, leaves, flowers, and fruit of odo- 

 riferous plants, giving them by their volatility their ^pecu- 

 liar odor. These oils are procured by distillation along 

 with water. They are called essences, and contain the con- 

 centrated odor of the plants. Thus otto or attar of roses fs 

 procured from the petals of various species of rose, especi- 

 ally Kosa centifolia; oil of peppermint from the leaves of 



