84 PROPAGATION OF PLANTS. 



As the heat and moiature come in contact with seeds the 

 materials of which they are composed well. and soften, 

 chemical changes follow, rendering the stored np matter 

 fit for nourishing the embryo. In albuminous seeds the 

 starch is changed into dextrine, thence to sugar, through 

 what may be termed the result of contact and the re- 

 arrangement of the molecules of the seed. Oxygen is 

 absorbed and heat generated, as may be seen on an ex- 

 tended scale in the operation of malting Barley and other 

 kinds of grain. In exalbuminous seeds slightly different 

 chemical changes occur, but all tend to the preparation 

 of nutriment for the embryo plant. It is quite evident 

 that the chemical changes that take place in sprouting 

 seeds QifteT as widely as do their chemical properties, but, 

 all are set inaction by the stimulus (heat) in the presence 

 qf moisture. ^^ 



The increase of heat accelerates germination, provided 

 it is not carried so far as to prevent the natural chemical 

 processes. A temperature of sixty-five to seventy-five 

 degrees may be considered a safe one for most kinds 

 of fruit, flower and vegetable seeds, but those with hard 

 ^hells or coverings, and especially those of tropical 

 origin, will usually require a higher temperature. In a 

 lower temperature, or less than fifty degrees, the necessary 

 chemical changes proceed very slowly, if at all, and often 

 cease altogether, even after having once commenced, and 

 when this occurs the seed usually decays, and for this 

 reason haste in sowing seeds in spring, and before the 

 ground is warmed by the sun and showers, often gives 

 unsatisfactory results. The germination of seeds is 

 governed by the same principles as that of the production 

 of buds from tubers, bulbs and even the emission of roots 

 from cuttings of ligneous plants, the starchy matter 

 stored up in the cells undergoing very similar chemical 

 changes in the reorganization and growth of the new 

 cells. 



