58 DISEASES OF PINES. 



Speaking generally, the Pines require light, open, and well-drained 

 soils, as deep as possible ; and many aspects of disease in them are due 

 to the non-fulfilment of these conditions. Unquestionably one of the 

 worst of these dangers results from the clogging of the soil at the roots, 

 whether due to wet clay, stagnant water, the covering up or hardening of 

 the surface e.g., by means of pavements, etc. or other processes. 



The general course of events is much the same in all these cases. The 

 primary cause of the injury is want of oxygen at the roots, for without 

 due supply of that gas in the water to which the living and absorbing 

 parts of the smallest root-fibrils have access the cells of the latter cannot 

 do their work. That is to say, the roots are unable to take up water 

 containing oxygen and mineral constituents in solution, at periods when 

 the " evergreen " leaves are transpiring large quantities of vapour into the 

 atmosphere. 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, etc., 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 appearance, 

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

 may even die. 



I have already shown how a very similar state of aifairs 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 con- 

 siderable acquaintance with the microscopic anatomy and physiology of the 

 plant, but anyone may readily grasp 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. 



Obviously young Pines in beds should not be exposed to powerful 

 insolation at a time when their roots are in hard frozen soil as above 

 described, and in those cases where such dangers are imminent a piece of 

 gauze or other shelter will reduce the chances of disaster. 



Equally obvious is it that suitable drainage operations may make all 

 the difference to a locality not quite fitted for growing such plants, and 

 I want to take this opportunity of insisting upon the very important 

 fact which applies to other plants as well as Conifers that the operation 

 of drainage does not consist in merely removing superfluous moisture ; far 



