20 APPLIED BIOLOGY 



In trying experiments with seedlings or with any full-grown plants 

 which have green color, keep the jar covered so as to exclude light. 

 The reason for this precaution will be clear in a later lesson which 

 deals with the effect of exposing plants with the green color to light. 



Other experiments connected with later lessons will give 

 further proof that plants breathe, and will help to explain 

 how they breathe. 



27. Plants have the power of reproduction. We are 

 familiar with the reproduction of many common plants from 

 seeds and of others from cuttings or slips (e.g., many house 

 plants, such as geranium, coleus, begonia). Many plants 

 (ferns, mosses, horsetails, mushrooms, etc.) form small 

 bodies, known as spores, from which new plants grow. 

 And many of the microscopic plants reproduce by automati- 

 cally dividing their bodies into two equal parts, and these 

 half-size plants soon grow to the full size. 



28. As in the case of animals, individual plants ultimately 

 die, but some plants may live to a very great age. Some of 

 the giant Sequoias of California, the largest of which are 

 nearly 300 feet high and more than 75 feet in circumference, 

 are probably at least two thousand years old, and some 

 botanists estimate over four thousand years. Some of the 

 famous oaks of Europe are believed to be eighteen hundred 

 years old, but our largest American oaks are probably less 

 than five hundred. There are in Europe specimens of chest- 

 nut, olive, cypress, yew, and other trees which are probably 

 much more than one thousand years old. It is impossible 

 to estimate accurately even after the trees are cut down and 

 the so-called " annual " rings of the trunk counted ; but 

 some of these trees were famous four or five hundred years 

 ago, and we may be sure that they are of far greater age 

 than any animals are known to have reached. 



29. Characteristic Life-Activities of Animals and Plants. 

 Our brief studies of a living animal and a plant have shown 

 us the following striking points of resemblance ; (1) the power 



