262 NEBRASKA STATE HORTICULTUUAL SOCIETY. 



finally settled into its present corrugated surface of moun- 

 tain, plain, and ocean basin, and the waters of the globe 

 rested in the depressions thus formed, there proved to be 

 enough water to fill these basins to a depth of six miles in the 

 deepest places and to cover just about three-quarters of the 

 surface of the globe. Now if there had been a little more 

 water in the make-up of our planet, so as to give a depth of 

 seven miles in place of six, the habitable regions of our planet 

 would have been reduced to a few islands in the mountainous 

 regions of the earth; if there had been still a little more, no 

 life could have developed on the earth of a higher type than 

 that of the deep-sea fishes. 



If, on the other hand, there had been a little less water, the 

 i^rth would have been an extended land surface with only 

 here and there an inland sea, and the greater part of it would 

 have been an arid waste like certain inland districts of the 

 larger continents today. 



2d. The points of melting and evaporation for water hap- 

 pen to lie within the ordinary range of terrestrial tempera- 

 tures, so that water is continually changing back and forth 

 from liquid to vapor and from vapor to liquid again, a most 

 admirable device for supplying water to crops of continental 

 extent. Prof. Percival Lowell, who has made so extensive a 

 study of the planet Mars, and who has urged so strongly its 

 probable habitability, points out the fact that on Mars it is 

 apparently very difficult for water to reach the point of con- 

 densation, that precipitation is therefore difficult and rare, 

 and for this reason the water problem for veg(4ation on Mars 

 is a serious one. 



3d. Water is one of the few substances in nature that ex- . 

 pands a little just at the point of solidifying; hence in the 

 process of freezing the crystals formed become slightly lighter 

 than the water in which they are immersed. They therefore 

 float instead of settling to the bottom, and the ice crust thus 

 formed protects the water below from being deeply frozen. 

 If water did not thus expand in freezing, the ice crystals 



