GENERAL PRINCIPLES AND METHODS. 137 



of heat and amount of moisture required are exceedingly 

 variable. As stated elsewhere, some seeds will germinate 

 at a temperature slightly above that of freezing water, 

 while others require nearly or quite a hundred degrees 

 Fahrenheit. Certain kinds of seeds will absorb more 

 than their own weight of water before sprouting or 

 bursting their hard, bony covering, while others appear 

 to retain, while ripening, nearly all the moisture required 

 in the early stages of growth. Seeds will withstand a 

 higher and a lower temperature in a dry atmosphere 

 than in a moist one, hence cool and dry, as well as hot 

 and dry, are non-inciting and preservative conditions for 

 most kinds of seeds. But seeds in general are not so 

 frail as to be readily destroyed by slight variation in 

 temperature, or in the hygrometric conditions of the 

 atmosphere, 'and their germination may usually be 

 hastened or retarded without serious injury, although it 

 is always safe to place seeds under conditions approxi- 

 mating those under which we find them in their native 

 habitats, but in order to do this we must know something 

 of their history. The spores of Cryptogamous plants 

 indigenous to a cold climate might quickly perish if 

 placed under the conditions most favorable for the growth 

 of a Cryptogam from the tropics, and the same difference 

 may often be noticed in the seeds of higher orders of 

 plants. With a knowledge of the peculiarities of the 

 climate of the habitat of plants, the propagator can usually 

 make a very close guess in regard to the treatment the 

 seeds require to insure germination. It is well, how- 

 ever, to bear in mind that latitude and longitude do not 

 furnish a very trustworthy guide to climate, for there are 

 snow-cupped mountains and very cool or cold regions of 

 country even in the tropics, or within the belt of country 

 so designated by degrees of latitude. Ocean currents 

 also have their influence, and the climate of widely sepa- 

 rated regions, on the same parallel of latitude, may differ 



