106 Observations on Liehig's " Organic Chemistry.^* 



should rather be of opinion that they never will. Were the 

 leaves the sole collectors of food at an advanced age of the 

 plant, whence does it arise that an old tree grows in so ex- 

 cessively vigorous a manner the first year after being cut over 

 by the ground, when there is nothing but roots to feed it. The 

 sugar and mucilage formed in the seeds, he also says, disappear 

 during the developement of the young shoots; and this I should 

 think soluble matter assimilated and rendered nutritive. This 

 action, he says, continues, and woody fibre is formed, leaves and 

 nourishment accumulate, till blossoms and fruit are produced by 

 the excess ; this he considers as a more compound transform- 

 ation, and illustrates his meaning by the instance of the double 

 elective affinity produced by the action of hydrocyanic acid and 

 water. It is probable that some very complicated chemical 

 process is at work in the production of blossom and fruit : but 

 that excess of nourishment is not the cause is a fact well known 

 to most practical gardeners, who, when they want fruit, give less 

 food, not more ; the more vigorous the growth of the tree they 

 know they will be obliged to wait the longer for fruit, unless 

 they proceed to mutilate the roots or branches. If the plant be 

 hi a pit, they stint by giving less water and less room ; if in the 

 ground, they cut some of the main roots, or depress or ring the 

 branches. 



The action of light and heat on the sap in leaves is re- 

 quired to produce in it a proper proportion of the elements 

 necessary to form flowers. If the sap is in great abundance, the 

 ordinary action of the leaves is not sufficient to produce this 

 proportion ; but when the proportion of leaves to sap is greater, 

 by lessening the quantity of sap, which has the same effect as the 

 extended stem and numerous arms and leaves of an old tree, to 

 which the soil cannot send a proportional quantity of food ; 

 when, by age or art, the quantity of sap is properly proportioned 

 to the action of the leaves ; that action is sufficient to produce 

 the proper proportion of the elements, and fruit is produced. 

 A warm summer in which there is much light and heat, or 

 rather the autumn, or a difference in climate, will produce the 

 same effect, and vice versa. Whether it is the action of this 

 concentrated sap on the organs that stimulates them to produce 

 flowers in place of leaves, or whether it is the presence of 

 proper food that enables the living power to form new organs, 

 the present state of our knowledge does not enable us to say; 

 analysis of the sap around flower-buds, and of the parts of 

 flowers themselves, might lead to some farther knowledge on 

 this point. It appears that the flower- bud, though formed, can be 

 changed, the pistils and stamens into petals, and the whole made 

 to return again to the form of leaves, by enriching the soil and 

 furnishing a greater quantity of soluble food, as is the practice 



