128 



JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



access the cells of the latter cannot do theiv work. That is to 

 say, the roots are unable to take up water, containmg oxygen and 

 mineral constituents in solution, at periods when the " evergreen " 

 leaves are transpiring large quantities of vapour into the atmo- 

 sphere. Consequently the young branches and tips of the tree 

 may die off rapidly, and if the source of mischief is permanent 

 the whole plant will die. 



But the class of diseases due to "wet feet" — as it is often 

 called — is even more complex than this. The persistent rotting 

 of dead rootlets in a wet soil not only implies loss of root-power 

 as above referred to ; it also entails the direct consumption of 

 oxygen and the fouling of the water by poisonous products of 

 decomposition, which diffuse through the dying tissues to higher 

 ones which were still healthy, and might have sufficed to supply 

 new rootlets &c. had the state of undue moisture been merely 

 temporary. 



Moreover, the presence of excessive moisture, and heavy wet 

 soils, prevent the necessary warming of the absorbing rootlets, 

 and cases are not uncommon where the stiffness and moisture of 

 a soil, though insufficient to cause the death of the absorbing 

 cells by asphyxia — i.e., the deprivation of free and dissolved 

 oxygen — or by direct poisoning, are still so powerful in preventing 

 the necessary rise of temperature, which must take place before 

 the absorbing living cells can obtain, and pass on, the proper 

 supply of water, which the losses from the aerial parts of the plant 

 demand, and by means of which the minerals needed can alone be 

 furnished, that symptoms of death by drought make their appear- 

 ance, the leaves turn yellow and then brown, shrivel and fall, 

 and the tree may even die. 



I have already shown you how a very similar state of affairs 

 may be brought about when young Pines have their aerial parts 

 exposed to dry air and hot sunshine, at a time when the soil is 

 frozen hard, and the roots are rendered inactive by the low 

 temperature of the ground. 



The proper understanding of all these matters in detail 

 requires considerable acquaintance with the microscopic anatomy 

 and physiology of the plant, but anyone may readily gather the 

 main points concerned, and will see that preventive measures 

 can only be put into action intelligently and with hopes of success 

 if these points are apprehended. 



