148 



DISEASES OF TREES 



the seedling the filamentous septate mycelium, which becomes 

 somewhat brown with age, produces tortuous lateral hyphae, 

 which ramify abundantly, apply themselves closely to the epi- 

 dermis (Fig. 84, a), and exercise a solvent action on the delicate 

 nbn-cuticularized epidermis. If one lifts up the hyphae it will 

 be seen that the epidermis has been dissolved at the points 



of contact. Without doubt mycelial 

 filaments also bore directly from these 

 points right into the plant. 



The stomata form a means both 

 of ingress and egress for the hyphae. 

 Such a stoma is depicted in Fig. 85, 

 which shows that the sides of the 

 depression leading to the stoma, and 

 the external walls of the epidermal 

 cells, are dissolved at the points where 

 the hyphae are or have been in close 



FIG. 83. Diseased pine seedlings. 



a, a specimen with dead roots ; 



b, ditto with a dead stem ; 



c, ditto with dead leaves and 

 buds. 



FIG. 84. A filamentous mycelium whose 

 lateral hyphae, a, come into close con- 

 tact with the epidermis ; &, a mycelium 

 which has developed in a nutrient 

 solution. 



contact. These places appear granulated because the ash con- 

 stituents of the cell-wall are either left wholly intact or are but 

 partially dissolved. I have proved that under the action of the 

 ferments exuded by wood-destroying parasites the cell-walls also 

 display granulation during the last stages of decomposition, and 

 for the same reasons as those just given. When a diseased 

 plant is investigated on the first symptoms of attack, a vigorous 

 growth of mycelium will be found in all the tissues. Although 

 the green cells do not part with their chlorophyll till some time 

 after death, they easily lose connection with each other, and the 



