136 MASSACHUSETTS HORTICULTURAL SOCIETY. 



look for the cause of our brilliant autumn colors to these chemical 

 changes? Coleiu is not to be confounded with that other color 

 material of plants, the well-known madder, so long used to dye the 

 color called Turkish red, which is a principle of the root and not 

 the leaf, — at least it is not stored in the leaf as are the others. 



These are dr^* facts, perhaps ; but ever since m}' earl}^ school 

 days I have noticed that the drier the fact the more solicitous 

 some one appeared to be that I should learn it. It now seems to 

 be my turn to present, or recall, a few dr\' facts to your minds. 



Thus w^e have the leaf, beautiful in its design, elaborate in its 

 construction, presenting the same general characters, whether 

 grown on the land or in the water, and varying in size from the 

 diminutive, almost microscopic, leaf to that of the renowned and 

 gigantic Victoria regia^ which, in the waters of its native Guiana, 

 presents a surface of eight, twelve, or even fifteen feet in 

 diameter. The attenuated leaves of the far northern forests, 

 although excelled by the profuse unfolding of those of the 

 tropics with their unending variety of form and coloring, and 

 anomalies of structure and habit, give us nevertheless the same 

 physiological conditions, which, briefly stated, are as follows, and 

 are all included under the term aeration, or respiration, which is of 

 the same vital importance in the vegetable world as it is in the 

 animal : — 



1. The absorption of carbonic acid (C Oo) from the air under 

 the stimulating influence of the sun's light. 



2. The absorption of oxygen (0) when the influence of the 

 sun's light is obscured or removed. 



3. The formation of carbonic acid by the union of the ox3-gea 

 thus obtained with the free or nascent carbon alread}" in the tissues. 



4. The assimilation of carbonic acid from whatever source it 

 ma}' be derived, which process, under the sun's light, decomposes 

 the carbonic acid, retaining the carbon ; and 



5. Eliminating the oxygen, — one of the greatest functions of 

 the leaf. 



6. The exhalation of carbonic acid when the sun's raj'S are 

 obscured, or darkness prevails. 



7. The reduction of the volume of sap by transpiration. 



We see b}' this enumeration that there are two phases of respira- 

 tion, seemingl}' directly opposed to each other, and evidently 



