REJUVENESCENCE IN NATURE. 219 



similar to that which occurs in animal respiration. It 

 is well-known that in the germination of mealy seeds, as 

 also in the sprouting of mealy tubers, an abundant ex- 

 cretion of carbonic acid is associated with the conversion 

 of the starch into sugar, and that this, connected with 

 perceptible evolution of heat, is caused by a decomposition 

 of sugar; it is well-known that beets and carrots lose 

 the sugar they contain, at the period of the unfolding of 

 the flower, which is accompanied with abundant excre- 

 tion of carbonic acid ; it is further known, through 

 Saussure's experiments, that the internal parts of the 

 flower, in the delicate tissue of which the formative 

 process deposits the smallest quantity of highly carbonised 

 substances, take up oxygen from the atmosphere and 

 excrete carbonic acid more abundantly than any other 

 parts of the plant ; again that the anthers are especially 

 distinguished among these, in which organs important 

 processes of solution of the tissue are connected with the 

 ulterior development of the pollen. In the nectaries 

 undecomposed sugar is excreted. There is no doubt but 

 all processes of solution and transformation in plants are 

 accompanied by excretion of carbonic acid. Observations 

 of the lower plants promises much more profit in this 

 respect. In Hydrodictyon I have seen cells in the stage 

 preparatory to the formation of gonidia (in which the 

 starch globules had already vanished), secrete gas bubbles 

 in unusual quantity ; I neglected to examine these 

 chemically, but they doubtless consisted of carbonic acid, 

 since they were visible very early in the morning and 

 later in the day when the sky was overcast, and since 

 other nets, in a vegetating stage, exhibited at the same 

 moments no such evolution of gas. 



The examination of the processes of solution and des- 

 struction, which we see introduce the new structure at 

 determinate turning-points of vegetable life, and which 

 are all characterised by absorption of oxygen and ex- 

 cretion of carbonic acid, leads us to the comparison of 

 the nocturnal respiration of plants, in which, according 



