hy Lindleys Theory of Horticulture. 44<5 



the whole system, may be easily comprehended by any. A slice 

 of any soft wood, as ash, will show the medullary rays ; and a 

 young transparent branch of a soft herbaceous plant, as the 

 dahlia, or a young seedling pine, will show the fibres to follow 

 from the cotyledons and leaves in an undeviating manner. 

 Whether every leaf sends down its fibres as far as the root 

 would be difficult to trace, as they generally penetrate under 

 those below them ; but that roots proceed from fibres is easily 

 seen on examining the cuttings of dahlias, of sorts which are 

 difficult to root. Before the roots issue, the white ends of the 

 fibres will appear, as if ready to protrude, and only retarded by 

 the too thick skin or epidermis, or the want of an accumulation, 

 of nourishing cellular matter at the bottom ; the cutting having 

 been too old, or too much hardened when taken off, either from 

 its age, or the nature of the sort inclining more early to harden 

 the epidermis. The theory of Dr. Darwin, however, of the 

 fibres forming roots, was too far carried, when it was asserted 

 the graft would change the nature of the stock, which practice 

 points out as incorrect. The shoot from the stock of the grafted 

 plant is always the same as the stock, unless by accident ; and. 

 the stock does not swell as the root does. The experiment 

 mentioned by Mr. Niven is uncommon. It may be possible that 

 a tree might live, for a time, with its bark and alburnum, to a 

 considerable depth, taken off for a considerable portion of the 

 stem all round, as said ; but that it would continue to live, and 

 be healthy, is hardly credible. It is the common practice in 

 America to kill trees in this way, by what they call girdling, to 

 save the trouble of felling. 



The section on the Action of Leaves is highly interesting and 

 instructive : their nature and uses are clearly and forcibly illus- 

 trated. The recovering of weak plants, and plants infested with 

 red spider, is greatly facilitated by keeping the back of the leaf 

 moist. Polyanthus, and other plants in pots, which are apt to 

 suffer in this way, are greatly benefited by reversing the plant, 

 and dipping the leaves in clear cold water. 



In the section Action of Flowers, there is much brought for- 

 ward that ought to be carefully studied. The production of flowers 

 proceeds from a highly concentrated state of the sap : what- 

 ever may be the quantity of sap produced, it must be perfectly 

 elaborated, before the petals, stamens, and pistils can be formed, 

 which are a higher state of existence than leaves. However great 

 may be the quantity of sap, if we have heat and light, and 

 action of the leaves to correspond, the flower and fruit, those 

 higher states of existence, will be formed ; and if the tree is 

 growing vigorously, whether from failure of the year's fruit, or 

 from being naturally vigorous ; and if the summer, but especially 

 the autumn, is warm and dry, to ripen the wood and concen- 



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