LECTURES AND ESSAYS. 429 



The change of the insoluble starch into soluble gum and sugars is brought 

 about by fermentation produced by the action of a ferment called diastase. 

 No fermentation can take place without the presence of germs, for whose 

 action a supply of air is necessary. It is thought that there is an oxidation 

 of carbon and an evolution of carbonic acid during the process of solution. 



Oxygen is also required for the assimilation of the dissolved food by the 

 growing parts. The greater portion of the young plant is made up of cellu- 

 lose. The glucose, or sugar, in solution is transferred to the growing por- 

 tion of the embryo, and uniting with oxygen forms cellulose, with an 

 evolution of carbonic acid. 



Carbonic 

 Glucose. Oxygen. Acid. Water. Cellulose. 



3 ( C 12 H 24°1 3 ) + 24 = 12 ( C0 2 ) + 14 ( H 3 0) + Ul2 H 2 O 10 



The other elements of the seed also become dissolved and transferred to 

 the embryo, and the process goes on, provided the conditions remain favor- 

 able, until the food supply is exhausted, or the plant is able to obtain 

 nourishment from outside sources. The radicle develops rootlets and sinks 

 downward, while the plumule pushes upward into the air and light, thus 

 completing the process of germination. 



In order to determine the value of old seeds, or of seeds purchased, it is 

 well to test their germinating powers before planting them. This can very 

 easily be done by anyone by wrapping them in cloth, placing them 

 between sheets of blotting paper, or in soil, and keeping them moist and 

 warm for a few days. 



It is thought by some that light is prejudicial to germination, and that 

 seeds must be covered in order to have them sprout. It has been found, 

 however, that the value of covering seeds was not owing to their deriving 

 any benefit from being in the dark, but because it enabled the planter to 

 regulate the heat and moisture, and, other things being equal, seeds germi- 

 nate just as well in the light as in the dark. 



The use of various gases and solutions of oxidizing substances has often been 

 recommended to hasten and assist germination, but no valuable results have 

 been obtained. It seems probable that common air and pure water contain 

 all the elements, in the exact proportions, required for the germination of 

 seeds. 



The time of sowing seeds and the depth of covering them are determined 

 by the foregoing principles. The quickest and best germination can be 

 obtained only when the soil has been warmed to the optimum temperature, 

 and ordinarily it will be found unwise to commit seeds to the soil until it 

 has an average temperature of 45° for such as peas, beets and radishes, and 

 55° for corn, squashes, and beans. 



The depth to which seeds should be covered is determined by the size of 

 the seed and the nature of the soil. Large seeds have a store of food which 

 will enable them to make their way through several inches of soil, and may 

 be planted deeply, which small seeds, if buried to any depth, would exhaust 

 their substance before reaching the surface, and a very slight covering, or 

 perhaps no covering at all, should be given them. 



In order to obtain the best results the seeds should be planted to a depth 

 which will secure them permanent moisture, as drying out would injure them 

 and if repeated several times might prove fatal to them. On light soils 



