180 



THE FLOHIST AMD POMOLOGIST. 



and it is now our business to see whether M. Robert's plan will effect this 

 result. 



In respect to the office of the bark of trees, Dr. Lindley describes the bark 

 to " consist of two distinct parts — the one external and cellular ; and the other 

 internal, resting upon the wood, and consisting of woody matter mixed with 

 cellular. The external is the rind or cortical integument ; the internal is the 

 liber ; when fluids leave the earth and pass into the stem in the shape of sap 

 it ascends by the woody matter of the finest fibres of the roots, haying left 

 them it flows into the new wood with which those fibres are connected, and 

 passes along this until it reaches the leaves. On its returning from them it 

 descends through the liber or outer bark in front, in part passing off hori- 

 zontally towards the centre through the medullary rays." 



We see then that the bark, and alburnum, or sapwood, form the important 

 medium of communication between the roots of trees, and their leaves; and 

 serve in fact as channels, conducting the sap upwards from the roots through 

 the alburnum or sapwood to their leaves, where, after its exposure to the in- 

 fluence of solar light and consequent change, it again descends principally 

 through the inner vessels of the liber or inner bark, but distributing itself by 

 means of horizontal cells throughout the whole system of the branches and 

 trunk. 



It will, therefore, be obvious that to remove this bark entirely, the channel 

 of communication whereby the carbonised sap is distributed through the 

 system of the tree will be cut off, and its peculiar functions as a medium for 

 transmitting the downward sap suspended until other channels can be formed ; 

 hnt as it is difficult to separate completely the outer from the inner bark, it 

 will frequently happen that when, to all appearance, the outer bark has been 

 removed, there will yet remain what maybe termed intermediate cells, capable of 

 conveying either the ascending or descending sap ; and which, on the removal 

 of the outer bark, are doubtless converted to the office for which there exists 

 the greater necessity, which in this case would be in conveying the sap down- 

 wards. But new bark has also been formed alone by the action of the 

 horizontal cells, which, in Exogens, communicate between the centre of trees 

 and the bark, as we have proved by direct experiment ; but the process is an 

 extremely slow one, and is named merely to show the efforts nature will make 

 to recover what has been lost. But in our opinion, neither the total nor partial 

 removal of the bark will effect a cure, and each tree so operated upon must 

 suffer in proportion as decortication has been more or less practised, and we 

 have the cause of all this still to deal with, for the cause of disease is deeper 

 seated. The attack of insects is owing to the effect of, and is, in no way 

 the primary cause of decay, which undoubtedly arises from various causes, 

 among which may be mentioned an undrained soil whereby the roots are 

 kept too wet and cold ; or they may suffer from the opposite cause— -i.e., when, 

 owing to an impervious surface, the natural rains which fall are carried away 

 and do not pass through the earth to supply the roots with moisture. Or a 

 contaminated atmosphere may exercise its baneful influence on the foliage, 

 and so induce decay. Want of proper nourishment or food in the soil is 

 another cause ; and last, but not least, the insidious attack of fungoid vegeta- 

 tion seizing on the roots of trees rendered inactive by a "cachexy" state of 

 system, owing to one or other of the above causes, just in the same manner as 

 the Scolytus attacks the trunk and branches under the same conditions. 



Drain your soil if water stagnates round their roots, or loosen the surface 

 so as to admit it to pass through where it remains in pools over their roots for 

 some time after rain. So that the roots may get the benefit of all the rain which 

 falls on the surface, which is frequently not the case in promenades, boulevards, 



