MATURATION OF THE FETTIT. 78 



the roots. It is, therefore, evident, that all causes, of 

 whatever nature, which interfere with the healthy 

 and regular action of leaves and roots, will also inter- 

 fere with the fruit. Or, if the leaves are placed in 

 such a manner with respect to the fruit, or at so great 

 a distance from it, that the fruit is unable to attract 

 food from them, it must either suffer or perish. This 

 explains why fruit formed upon naked branches will 

 not continue to grow ; ,and why the presence of a leaf 

 immediately above a fruit, on the same branch, is so 

 beneficial to it. The size and excellence of fruit will 

 hence be in proportion to the abundance of organisa- 

 ble matter prepared and stored up in its vicinity.* 

 97. Although fruit has, in common with leaves, 



* The accumulation of sap, and its consequent viscidity, may, 

 however, he attended with disadvantage to a plant, as really hap- 

 pens in the Potatoe, the most farinaceous varieties of which are 

 liable to a disease called the " curl." Mr. Knight attributed this to 

 the inspissated state of the sap, which, he conceived, if not suffi- 

 ciently fluid, might stagnate in and dose the fine vessels of the leaf 

 during its growth and extension, and thus occasion the iiTegular 

 contractions which constitute this disease. He therefore suffered 

 a quantity of Potatoes, the produce almost wholly of diseased 

 plants, to remain in the heap, where they had been preserved dur- 

 ing winter, till each tuber had emitted shoots of three or four inches 

 in length. These were then carefully detached, with their fibrous 

 roots, from the tubers, and were committed to the soil, when, having 

 little to subsist upon except water, not a single curled leaf was pro- 

 duced, though more than nine tenths of the plants which these 

 identical tubers subsequently produced were much diseased. The 

 same effect has been produced by other persons, by taking up 

 the tubers intended for seed before they were full grown, and con- 

 sequently, before the excessive inspissation of their secretions had 

 taken place. 



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