PLANT BIOLOGY 



CHAPTER I 

 GENERAL INTRODUCTION 



1. Lifeless Things and Living Things. As we look about 

 us, we find that the world in which we live is wholly composed 

 of two classes of things, which we commonly speak of as 

 living things and lifeless things. Soil, air, and water, for 

 example, we know to be lifeless. Water is probably the 

 simplest of these three so far as its composition is concerned. 

 Soil, on the other hand, is very complex in composition, being 

 formed of nearly all the substances known to the scientist. 

 Enveloping the earth is a mixture of gases called the atmos- 

 phere which extends outward in every direction for a dis- 

 tance of about fifty miles. Everybody knows, too, that over 

 the surface of the earth, in the water, and even in the air 

 are countless numbers of living things which we designate 

 as either plants or animals. 



One might think that it would be an easy matter to set 

 down the characteristics by which living things are dis- 

 tinguished from those that are lifeless. And such is the case 

 when we compare a rock in a field with a horse that is feeding 

 beside it. Unlike the animal, the lifeless rock is unable to 

 move itself, it neither eats nor breathes, and it gives no 

 evidence of feeling or of will power. 



But suppose we select for comparison a railroad locomotive 

 and a horse. Both move ; both need a plentiful supply of air ; 



