132 Introduction to Botany. 



part immediately employed in the work of the protoplasts, 

 and in part lost to the plant in the form of heat by radia- 

 tion and conduction, and in the evaporation of water from 

 the tissues. The internal energy which appears during 

 respiration was obtained for the most part from the sun 

 during the process of photosynthesis, and in part from the 

 salts from the soil, and stored within the plant in the form 

 of potential energy in starch, sugar, proteids, etc. ; and as 

 active energy from the sun was required to form these sub- 

 stances, so now it is evolved when they are broken down 

 by oxidation. If we are to understand the essential thing 

 about photosynthesis, we must perceive it as a process of 

 storing the sun's energy in such a form as to make it 

 available to plants by night as well as by day, and through- 

 out all seasons of the year. 



104. Oxidation a Vital Process. The process of respira- 

 tion is not a passive oxidation, but is induced, and to a 

 certain extent regulated, by the living protoplast. In 

 plants, however, the regulation of oxidation is not by any 

 means so exact as in warm-blooded animals, whose tem- 

 perature is allowed to fluctuate only within very narrow 

 limits, while the temperature of plants under normal con- 

 ditions seldom differs much from that of the surrounding 

 atmosphere. 



105. Annuals, Biennials, and Perennials. A large class 

 of plants bears seeds the first year, and in so doing these 

 plants send into the seed so much of their stored energy 

 that they are unable to survive the winter, or in some cases 

 even to continue to the end of the summer. Such pi? its 

 are known as annuals. Many other plants store up the 

 energy accumulated by photosynthesis in underground 

 parts, such as tubers, bulbs, etc., and having survived the 

 winter produce their seeds and die at the end of the second 



