FROZEN-SAP BLIGHT. 325 



Again, loses its vitality, and becomes dark and discoloured, and, 

 in some cases, so poisonous, as to destroy the leaves of other 

 plants, when applied to them. Here, along the inner bark, it 

 lodges, and remains in a thick, sticky state, all winter. If it 

 happens to flow down till it meets with any obstruction, and re- 

 mains in any considerable quantity, it freezes again beneath the 

 bark, ruptures and destroys the sap-vessels, and the bark and 

 some of the wood beneath it shrivels and dies. 



In the ensuing spring, the upward current of sap rises 

 through its ordinary channel the outer wood or alburnum the 

 leaves expand, and, tor some time, nearly all the upward current 

 being taken up to form leaves and new shoots, the tree appears 

 flourishing. Toward the beginning of summer, however, the 

 leaves commence sending the downward current of sap to in- 

 crease the woody matter of the stem. This current, it will be 

 remembered, has to pass downward, through the inner bark or 

 Zz'Jer, along which, still remain portions of the poisoned sap, 

 arrested in its course the previous autumn. This poison is di- 

 luted, and taken up, by the new downward current, distributed 

 toward the pith, and along the new layers of alburnum, thus 

 tainting all the neighbouring parts. Should any of the adja- 

 cent sap-vessels have been ruptured by frost, so that the poison 

 thus becomes mixed with the still ascending current of sap, 

 the branch above it immediately turns black and dies, precisely 

 as if poison were introduced under the bark. And very fre- 

 quently it is accompanied with precisely the odour of decaying 

 frost-bitten vegetation.* 



The foregoing is the worst form of the disease, and it takes 

 place when the poisoned sap, stagnated under the bark in spots, 

 remains through the winter in a thick semi-fluid state, so as to 

 be capable of being taken up in the descending current of the 

 next summer. When, on the other hand, it collects in sufficient 

 quantity to freeze again, burst the sap vessels, and afterwards 

 dry out by the influence of the sun and wind, it leaves the 

 patches of dead bark which we have already described. As 

 prart of the woody channels which convey the ascending sap 

 probably remain entire and uninjured, the tree or branch will 



* We do not know that this form of blight is common in Europe, but the fol- 

 lowing extract from the celebrated work of Duhamel on fruit trees, published in 

 1768, would seem to indicate something very similar, a long time ago. 



" The sap corrupted by putrid water,or the excess of manure, bursts the cellu- 

 lar membranes in some places, extends itself between the wood and the bark, 

 which it separates, and carries its poisonous acrid influence, to all the neighbour- 

 ing parts, like a gangrene. When it attacks the small branches, they should be 

 cut off; if it appears in the large branches or body of the tree, all the cankered 

 parts must be cut out down to the sound wood, and the wound covered with com- 

 position. If the evil be produced by manure or stagnant water, (and it may be 

 produced by other causes,) the old earth must be removed from the roots, and 

 fresh soil put in its place, and means taken to draw off the water from the roots. 

 But if the disease has made much progress on the trunk, the tree is lost " Traite 

 des Arbres Fruitiers. vol. 11, p. 100. 



28 



