126 



DISEASES OF TREES 



The above report refers only to conifers attacked by the 

 parasite. Professor Crie of Rennes was good enough to send me 

 more than once the roots of diseased plants of Castanea vesca. 

 On one of these I found Rhizina undulata luxuriantly developed. 

 On removing a diseased or dead plant from the ground, one 

 will find that a large quantity of sandy soil is firmly held 

 amongst the roots by means of numerous fungus-filaments, but 



that no outpouring of resin what- 

 ever is visible (Fig. 65). 



On the roots being isolated 

 and carefully examined, it will 

 be found that peculiar mycelial 



FIG. 65. The roots of a silver fir 

 which has been killed by Rhizina. 



FIG. 66. Mycelial growths resembling 

 Rhizoctonia, which are met with on 

 the roots of plants infested by 

 Rhizina, magnified by 3. Mycelial 

 strands protruding from the cut sur- 

 face in moist air. Natural size. 



bodies resembling Rhizoctonia project from the cortex. At a 

 distance of two to three fifths of an inch these begin to ramify, 

 and ultimately divide into filamentous mycelia (Fig. 66). If 

 one cuts off a root and makes a culture in a moist chamber, it 

 will be found that such mycelial bodies will form in large numbers 

 on the cortex, or on the cut surface of the wood. These ramify 

 in the usual way and end in a fine point (Figs. 66 and 67), 

 and are always brilliantly white in colour. 



A microscopic investigation will reveal the cause of this 

 colour, which is due to drops of ethereal oil adhering in great 

 numbers to the external filaments, or to the apices of the fine 



