THE CANADIAN nORTICULTUKIST. 



1S5 



tlows so freely in the spring is com- 

 posed largely of water absorbed by the 

 roots of the jilant. This water holds 

 in solution miiiute quantities of gas 

 and mineral salts, and adds thereto, on 

 its upward way, dextrine and sugar, 

 which it dissolves out of the cells as it 

 comes in contact with them, gaining in 

 density as it nears the leaf. Within 

 the leaf it parts with much of its water, 

 having no longer a use therefor, receiving 

 in its }dace carbon and the digested 

 juices acted upon by the chlorophyl, as 

 it passes through the surface of the 

 leaf, thence by the leaf stalk into the 

 cellular and woody tissues of the bark, 

 and continuing its downward ]>assage, 

 making deposits of food first in the 

 cells of the pith, at the base of every 

 incipient bud, then a copious store in 

 the cambium regions, giving also a good 

 portion to the medullary rays, some to 

 be carried outward to the cortical layer, 

 and some onward for solidifying the 

 wood, and, lastly, the richest portion is 

 sent to the root, every branch and fibre 

 being filled. The }-eturn sap also con- 

 tains nitrogen to a limited extent, and 

 minute portions of mineral matter. 

 From this nitrogen is first oi-ganized 

 the protein substances analogous in 

 composition to the living tissues of 

 animals, and cellulose, the peculiar 

 principle of vegetable tissue, having in 

 it the exact elements of watei-. The 

 action of chloi-ophyl upon this substance 

 develops gum, sugar and starch, which 

 are nutritive products common to all 

 plants, and are stored away for future 

 use, as fat is stored away in our own 

 and all animal systems. As examples, 

 we have sugar stored up in the root of 

 the beet and in the stalks of corn, 

 sugar-cane and sorghum, and starch in 

 the tubers of the potato. These sub- 

 stances, with cellulose, are all com- 

 posed of carbon with the elements of wa- 

 ter, often in identical proportions, and 

 ai'e easily converted into one another. 



2 



The leaf is not alone an interesting 

 study because curious, but it has had 

 no little part in rendering the world 

 habitable for man. If this consisted 

 only of the mineral portion it would be 

 only a rocky desert, but mingled with 

 the mineral we find the organic matter, 

 which consists of the remains of former 

 tribes of plants and animals, and the 

 products of this decomj)Osition, cai'boniu 

 acid and ammonia. But as this earth 

 sujjported vegetable life before it did 

 anunal existence, we see the important 

 j)lace given to our little leaf. Age aftei 

 age it went on elaborating the juices ot 

 plants, leaving for the final decay that 

 comes to all to add their organisms to 

 the soil, making it such as we have it 

 to-day, a life-supporting element, giviny 

 occupation to a large majority of 

 civilized men. 



But it is not soil alone that has been 

 created by the instrumentality of oui 

 hastily surveyed leaf. The stores of 

 coal and petroleum, enough to last for 

 centuries to come, were formed from 

 gigantic pines, ferns and lycopods, which 

 were developed through the agency of 

 leaves. It is probable that at the epoch 

 of growth of these enormous primeval 

 foi'csts the atmosphere was much more 

 highly charged with carbonic acid than 

 now, and that from this source the 

 gigantic lycopods, ferns and conifers 

 were develo[)ed, thus converting into 

 organized products an immense amount 

 of carbonic acid which had ^^ireviously 

 been liberated by some change in tln:- 

 mineral world, and by its removal from 

 the atmosphere the earth was prepared 

 for the residence of a higher class oi' 

 animals than had previously existed. 

 It is regarded by scientists as a fixed 

 fact that the whole vast accumulation 

 of carbon now in the earth was at one 

 time a component part of the atmos- 

 phere. 



In answer to the practical question 

 how farmers and horticulturists are to 



