EVOLUTION AND VARIATION 55 



of nature, such as gravity, heat, and light; in 

 other words, have the quality of positive and 

 negative reactions — a limited power of choice; 

 and from such faint prophecies of life, just 

 emerging from the realm of chemistry, have 

 come during aeons of time all the varied plant 

 and animal life on this earth, including man 

 himself. 



In a review of the fundamentals of life, we 

 may fairly commence with the crystal forms. 

 Crystals grow when surrounded by a solution 

 which contains abundant nourishment in a tem- 

 perature adapted to the species, but from the 

 outside, very much like plants and trees in which 

 the nourishing leaf -digested protoplasmic sap 

 flows down, usually in the cambium between the 

 bark and wood, adding thin layers of growth 

 very much after the manner of silver plating, or 

 sedimentation in muddy water. 



.Crystals, like plants and animals, grow into 

 certain specific forms which may vary to a cer- 

 tain extent to accommodate themselves to their 

 environment, for heredity and environment must 

 be reasonably well fitted to each other, or life 

 always ceases to exist. The internal heredity 

 (formerly acquired) forces and the external or 

 environmental forces must be adapted to meet 

 each other somewhat as a garment fits the body. 



