DEVELOPMENT OF HEAT. 539 



new storm casts the whole tree to the ground, separates the trunk from 

 the roots, and it perishes of hunger. 



In all the perennial plants there is a peculiar condition to be observed 

 which is connected with reproduction, and which has before been men- 

 tioned. In the simple plant a mass of cellular tissue is formed which 

 maintains a connection between the new individuals originating in the 

 formation of buds, and thus renders possible the existence of a compound 

 plant. In this way, individuals originating from seeds remain either 

 living, and continue to grow on, as is the case in most trees, or the plant 

 dies completely down, and leaves behind it only these masses of cellular 

 tissue which, although living, are incapable of individual development, as 

 is the case in undershrubs. In trees this mass of cellular tissue is the 

 cambium of the stem ; in undershrubs it is that of the rootstock. 



In the remaining (simple) plants we see thus much, that a plant whose 

 terminal bud is completely changed into reproductive organs must have 

 reached the end of its life, and cannot continue to grow. How it is that 

 death occurs in simple plants, which only develope their lateral buds into 

 flowers, is not yet understood. There is a negative explanation, which 

 is, that it depends on an exhaustion of the vital powers through the 

 development of the flowers ; but, as we have no definite conception of 

 what these particular vital powers are, we can hardly regard this as an 

 explanation. Much more must be done before we can draw correct con- 

 clusions. 



I know of no book, whether on Vegetable Physiology or on Botany in 

 general, in which the question of the death of" the plant is more than 

 incidentally mentioned. Unger and Endlicher have given a chapter on 

 the subject in their " Grundziige," which was published after my own 

 observations, and contains similar remarks. 



SECTION II. 



SPECIAL PHENOMENA IN THE LIFE OF THE ENTIRE PLANT. 



A. Development of Heat. 



211. The temperature of the living plant scarcely ever cor- 

 responds with that of the surrounding atmosphere. 



The following three relations have hitherto been observed : 



A. Germinating seeds (ofthePhanerogamia) develope a heat which 

 considerably exceeds that of the surrounding atmosphere. This is 

 most probably owing to the process of combustion in the forma- 

 tion of carbonic acid and water during the decomposition of the 

 assimilated matters, starch, oil, &c. 



B. Trees of our climate exhibit in their interior a variable tem- 

 perature, being higher in the winter and lower in the summer than 

 that of the surrounding atmosphere. These changes are always 

 strictly in accordance with the changes of the atmosphere in their 



