GERMINATION. 115 



Soeds buried deep in the soil Avill not germinate, but on ex- 

 posure to the air immediately spring up. Turnip-seeds have 

 been eight years in the soil. Seeds taken from a pit, in wliich 

 condition they had lain hundreds of years, germinated readily. 

 This fact probably explains the springing up of different trees 

 when a forest is cut down and the ground broken up. A weak 

 solution of chlorine hastens germination, probably by aiding the 

 decomposition of water. 



206. Heat is another necessary condition on which germina- 

 tion depends. Germination cannot take place in a temperature, 

 unless some degrees above freezing, and it may take place in a 

 temperature which would be entirely inadequate to the per- 

 fection of its growth. If tlie temperature is too high, the 

 seeds may germinate, but unhealthy action is produced, and 

 the plant perishes by over-action, produced by this powerful 

 agent. 



It has been found that Wheat, Barley, and Rye would ger- 

 minate at 44 degrees Fahr., which is about the lowest point it 

 would take place. These grains being composed in a great de- 

 gree of starch, and at the expense of which germination proceeds, 

 it was thought that these seeds would sustain any temperature 

 as high as the grains of starch would, without bursting their in- 

 teguments. Under ordinaiy^ circumstances this takes place at a 

 little above 167°, but this temperature was found sufficient to 

 destroy the vitality of the various grains. Beans, Peas, and like 

 seeds. Many lost their vitality at 125° and some as low as 

 113°, temperatures w^hich the surface of our soil often exceeds. 

 These facts teach us the necessity of shading, or of planting our 

 flower and delicate garden seeds in cool places, wdien it is done 

 after the warm days of our spring come on. Much of the vitu- 

 peration against seedmen would be saved by this course. Dark- 

 ness is favorable to germination ordinarily. The yellow rays are 

 most injurious, while the blue accelerate the process, containing 

 as they do the actinic or chemical rays. 



207. When the three agents above noticed are brought to 

 act upon the seed in due proportion it begins to swell, bursts its 

 integuments, generally by the protrusion of a radicle, which 

 takes its direction downward, and soon after the plumula or stem 

 makes its appearance and takes its course upward. During 

 germination considerable heat is generated, no doubt the effect 



Examples. Wliut fact does it explain ?— 20(5. How is orcrmiimtion affected 

 by temperature ? At how lii.<,'h or liow low temperature will seeds trer- 

 minatef At what temperature do many seeds lose their vitality ? Wliat 

 do these facts teacli us ? How does darkness affect srermination ?— 2u7. 

 How docs germination proceed » What is generated durin<; the process i 



