TOS JOURNAL OF FORESTRY 



SILVICULTURE, PROTECTION, AND EXTENSION 



Specialization, or the act of specializing by para- 



Parasitic sitic fungi, is the result of cooperation between 



Fungi their individual capabilities and the nature of the 



locality, that is, of the host plant. However, they 



are so much more dependent upon their hosts, since they must not 



only derive water and rriineral constituents, but also carbon compounds, 



from them and with reference to the latter, host plants exhibit the 



greatest variation. Combinations of carbon may be considered under 



three forms: (1) Protoplasm, with cell nucleus and chloroplasts ; 



(2) cell sap with its free carbon compound contents; (3) cell-wall. 



The cell-sap constitutes the most convenient source of nourishment 

 for the parasites. The power of the parasite to attack the cell-sap 

 is altogether dependent upon its ability to kill the protoplasm. It is 

 well known, however, that the permeability of living protoplasm is 

 secured by chemical action and the so-called life energy which enables 

 a plant to withstand a fungous attack can be called "protoplasmic 

 permeability." Insofar as "life energy" of a plant denotes rapidity 

 of growth and normal anatomical development, the fact that sickly 

 and weak plants are especially subject to attack is due to other causes. 

 Slow growth leaves plants longer in the condition of young growth with 

 greater sap content and incomplete development of the protecting cell 

 walls ; weak resin pressure in conifers afTects parasites less than a 

 vigorous exudation of this protecting medium which assists the host 

 in combating both insects and fungi. It is evident that not all cell-sap 

 possesses a like food value for fungous growth. Many poisonous ele- 

 ments in cell-sap are not capable of nourishing certain fungi ; whether 

 they are actually poisonous to the fungi is not definitely known. 



Specialization is first brought about in the ability of the fungus to 

 penetrate the cell-wall which ofifers the chief medium of resistance. 

 The most difficult wall to overcome is the thin corky layer, the cuti- 

 cula which frequently covers the outer side of epiderminal cells. Very 

 frequently the cuticula ofifers a poor place for the germination of 

 spores because is may shed dewdrops and rainwater. It is also, more 

 or less, insusceptible to chemical action. Entrance in some cases is 

 effected through mechanical boring with a sort of needle appendage 

 or with the help of chemotropic stimuli. Entrance is often effected 

 through the stomata. 



Among others, one of the most important fungi which brings about 

 the destruction of forest trees chiefly because of its ability to decompose 



