162 ARM ILL ARIA MELLEA, 



Brefeld found that his older cultures produced a profusion 

 of aerial rhizomorphs of the subterranean type. When 

 these were growing strongly he dug up some thick roots of 

 Scots pine and brought them undamaged and fresh into 

 .close contact with the apices of the rhizomorphs (' Ich grub 

 sie aus und brachte sie unverletzt und frisch mit den Rhizo- 

 morphenspitzen in innige Beriihrung '). His figures show 

 that the pieces of root were only about 4 in. long. Brefeld 

 found that the rhizomorph apices grew into the roots very 

 quickly, both through the cut ends and through the un- 

 damaged bark. The time that they took to penetrate by 

 each route is not stated. 



Now, when digging up fairly thick pieces of root it is 

 very difficult not to damage the bark, so that in this experi- 

 ment the rhizomorphs may have grown in through wounds. 

 Also cut pieces of roots, especially of coniferous roots, 

 quickly lose their vitality and even after a very short time 

 cannot be described as healthy roots. Brefeld says that 

 the rhizomorphs grew in at once (' sofort '), but the possi- 

 bility is not excluded that the first rhizomorphs to enter 

 gained admission through the cut end, whereas the others 

 may have taken some days about it. It should not be 

 taken, then, as proved that rhizomorphs can force their 

 way into a healthy root through undamaged bark. 



The evidence gained from my own observation supports 

 the view that the rhizomorphs can only attack through 

 damaged or dead roots. Take the following instance. In 

 Bagley Wood, near Oxford, a series of quarter-acre experi- 

 mental plots were planted in 1907. Various species of 

 conifers were used, and my observations, which date from 

 191 3, show that most of the area is infected with Armillaria. 

 At certain points there are large stumps from which rhizo- 

 morphs radiate in all directions, and some thousands of 

 the toadstools appear annually on and around these stumps. 

 The fungus was found in plots containing each of the follow- 

 ing species : Corsican pine, Weymouth pine, Norway and 

 Sitka spruce, larch, and deodar, and yet, with the exception 

 of some fifteen Weymouth pines and a number of Sitkas, 



