184 



THE CANADIAN HORTICCLTDRIST. 



chemists can tell us very little about it. 

 They have not yet ascertained its com- 

 ponent elements, and cannot tell whe- 

 ther it contains iron or nitrogen ; but 

 can only say that it is never produced 

 in the absence of compounds capable of 

 supplying these elements. It is possi- 

 ble that it may consist of more than 

 one substance, or that the 1 'af green of 

 all plants may not be identiua,! in every 

 respect. Chlorophyl is found in those 

 cells of plants where the absorption and 

 decomposition of carbonic acid gas goes 

 on, with which process of vegetable life 

 it is closely connected. 



A second coloring matter is found 

 common also to fruits and flowers, as 

 in the leaves oi the red cabbage, the 

 skin of the grape, and in the dahlia, 

 and is called colein, from Ooleus, a genus 

 of plants in many species of which it 

 occurs abundantly. It is very irregu- 

 larly distributed, and might be called 

 one of the curiosittes of the leaf, as it 

 has no important offices to fulfill therein. 

 In chemical composition it is identical 

 with the coloring matter of red wine, 

 most red, blue and purple flowers and 

 fruits, and the red pigment of some of 

 the varieties of the beech. It should 

 not be confounded with the coloring 

 material of the well-known madder, so 

 long used to dye Turkey red, which is 

 a principle of the root and not the leaf — 

 at least it is never stored in the leaf. 



Thus we have the leaf, beautiful in 

 its design, elaborate in its construction, 

 presentmg the same general characters, 

 whether grown on the land, in the air, 

 or in the water, and vai'ying from the 

 diminutive leaf, almost microscopic, to 

 that of the renowned Victoria regia, 

 which in the waters of its native Guiana 

 presents a surface of from eight to 

 twelve or even fifteen feet in diameter. 

 The attenuated leaves of thefar N"orthern 

 forests, counterbalanced by the profuse 

 unfolding of those of the heated tropics, 

 with their unending variety of form and 



coloring, and anomalies of structure 

 and habit, all give us the same physio- 

 logical conditions, which, briefly stated, 

 are as follows, and are all included 

 within the tei'm aeration, or respiration, 

 which is of the same vital importance 

 to the vegetable world as it is to the 

 animal : 



First — The absorption of carbonic 

 acid from the air under the stimulating 

 influence of the sun's light. 



Second — The absorption of oxygen 

 when the influence of the sun's light is 

 obscured or removed. 



Third — The formation of carbonic 

 acid by the union of this oxygen with 

 tlie free or nascent carbon already in 

 the tissues. 



Fourth — The assimilation of carbonic 

 acid from whatever source it may be 

 derived, which process, under the sun's 

 light, decomposes the carbonic acid, 

 retaining the carbon, and 



Fifth — -One of the greatest functions 

 of the leaf, eliminating the oxygen. 



Sixth — The exhalation of carbonic 

 acid when the sun's rays are obscured 

 or darkness prevails. 



Seventh — The reduction of the vol- 

 ume of sap by transpiration. 



We see by this enumeration that 

 thei'e are two phases of respiration, 

 seemingly directly opposed to each 

 other, and evidently occasioned by the 

 light and heat of the sun. Surely we 

 ought to derive satisfaction from the 

 thought that as we tOl our fields during 

 the intense heat of the summer sun, 

 the same sunlight that exhausts us is 

 giving us more oxygen to breathe, and 

 is storing up food for our future sus- 

 tenance in the plant we cultivate. The 

 thought may not render the toil less 

 fatiguing, but the consolation comes 

 from the knowledge that we shall get 

 the upper hand of Nature when we 

 harvest the crop. 



To understand the full ofiice of the 

 leaf we must know that the sap which 



