352 HOW CHOPS GKOW. 



For the agricultural plants cultivated in New England, 

 a range of temperature of from 55° to 90° is adapted for 

 healthy and speedy germination. 



It will be noticed in the above Table that the seeds of 

 plants introduced into northern latitudes from^ tropical 

 regions, as the squash, bean, and maize, require and 

 endure higher temperatures than those native to temper- 

 ate latitudes, like wheat and barley. The extremes given 

 above are by no means so wide as would be found were 

 we to experiment with other plants. Some seeds will 

 germinate near 33°, the freezing point of water, as is 

 true of wheat, rye, and water-cress, as well as of various 

 alpine plants that grow in soil wet with the constant 

 drip from melting ice. On the other hand, the cocoa- 

 nut is said to yield seedlings with greatest certainty when 

 the heat of the soil is 120°. 



Sachs has observed that the temperature at which 

 germination takes place materially influences the relative 

 development of the parts, and thus the form, of the seed- 

 ling. Very low temperatures retard the production of 

 new rootlets, buds, and leaves. The rootlets which are 

 rudimentary in the embryo become, however, very long. 

 On the other hand, ve^ high temperatures cause the 

 rapid formation of new roots and leaves, even before 

 those existing in the germ are fully unfolded. The 

 medium and most favorable temperatures bring the 

 parts of the embryo first into development, at the same 

 time the rudiments of new organs are formed which are 

 afterwards to unfold. 



* Wheat, and probably barley, may, occasionally, germinate at, or. 

 very near, 32°. 



