80 



BRITISH FOREST TREES. 



rior increasing stool and hard-pressed earth under- 

 neath it ; this earth at the same time becoming ex- 

 hausted of the particular pabulum of the plant. It 

 is, therefore, quite probable, from these parts of the 

 roots being the weakest, that they will be most sus- 

 ceptible of injmy from being soaked in stagnant wa- 

 ter in the flat tills ^, starved during droughts in light 

 sand, tainted by the putrid vapom's of rich vegetable 

 mould, or poisoned by the corrosive action of perni- 

 cious minerals. It may also be supposed that these 

 smothered sickly roots, not possessing sufficient power 

 or means of suction (endosmose), will be left out in 

 the general economy of vegetation of the plant, thence 

 lose vitality, and become corrupt. But this affords 

 no explanation why the larch roots, under these cir- 

 cumstances, are more liable to corruption than those 

 of other trees, or how the bulb itself should become 

 contaminated. 



* When water is stationary, either in the pores of the soil or by 

 itself, if the temperature be not very low, a slight putrefaction ge- 

 nerally commences, aided by the dead vegetable or animal matter 

 contained in the soil or the water ; and it is only the more robust 

 aquatic vegetables whose juices are not corrupted, from their roots 

 being soaked in this tainted fluid. It would appear, too, that the 

 aqueous part of the atmosphere is also susceptible of the same pu- 

 trid changes, although in general the putrescency may have com- 

 menced before the evaporation. This condition of the aqueous 

 part of the atmosphere is a disposing cause to blight or mildew in 

 vegetables, and remittent, intermittent, and putrid fevers in man. 

 Mill-ponds are notorious both for mildew and agues. 



