10 LIFE S BEGINNING ON THE EARTH 



this type of growth which is so typical of the non-living 

 world. A crystal grows by slow gradual apposition of 

 diminutive particles — molecules — -each of which has the 

 same shape. They are attracted to the surface and at- 

 tached to it in such a manner that the whole crystal main- 

 tains its shape, no matter how much it grows. Yet these 

 particles are so small that they cannot be seen even with 

 the highest power of magnification available; hence there 

 is no visible break in continuity in the appearance of the 



Fig. 1. Snow Crystals 



Note the sharp edges and smooth planes of these crystals. All these 

 different forms arise by the combination of small ice crystals in various 

 ways. Similar crystals are formed when any dissolved solid substance 

 like sugar or a salt settles from its solution in water, if the water is slowly 

 evaporated. 



crystal. This is the generally accepted explanation of 

 crystalline growth. Science may still rind unsolved prob- 

 lems here as everywhere, but undoubtedly the process is 

 not nearly as involved as that of the growth of a plant or 

 animal. 



The problem is whether any similarity can be found be- 

 tween the growth of a crystal and the growth of living or- 

 ganisms. The perfectly smooth planes and sharp angles of 

 a crystal are, of course, quite unlike the general appearance 



