VEGETATION. 341 



into sugar in plants? 464. What is the difference between the artificial 

 and the natural production of sugar ? 465. How does the bee form honey ? 

 466. What is manna ? What are its ingredients ? Its properties ? What 

 is said of the manna of the Israelites? 467. What is the use of gluten in 

 plants ? How may gluten be obtained from wheat flour ? Why is gluten 

 called vegetable fibrin ? 468. What is said of vegetable albumen ? 469. 

 What of casein ? How may it be obtained ? 470. What is said of protein 

 substances ? Why are they called plastic elements ? What is the mean- 

 ing of the term azotized ? 



CHAPTER XXVIL 



VEGETATION. 



471. The Seed. The beginning of the formation or build- 

 ing up of a plant is in certain operations in the seed. The 

 chemical forces remain dormant in the seed until awakened 

 to action by heat and light. These, in the presence of 

 moisture and air, operate upon the seed when it is put into 

 the ground. "With these stimuli wholly shut out seeds 

 may be kept a very long time in their dormant state, their 

 living power being preserved in the sleep. Thus seeds 

 which were found buried in the ruins of Herculaneum were 

 proved to be alive by growing when they were planted, 

 like the fresh seeds of the previous year. 



On the whole our knowledge of the chemical operations 

 taking place in the plant is very slight; only here and 

 there have we glimpses of wonderful processes which pro- 

 duce such an immense variety of vegetable bodies. 



472. Growth from the Seed. A seed is composed chiefly 

 of starch, with some gluten. Both of these are insoluble 

 in water, and therefore can not be used in growth until 

 they are so changed as to be rendered soluble. Accord- 

 ingly the first thing which is done by the forces men- 



