Page 42 



BETTER FRUIT 



April 



obtained, make a rapid growth. They 

 may soon form countless numbers of 

 delicate branches which are invisible to 

 the naked eye, or may become abundant 

 enough to form many white strands, 

 white sheets or the cord-like black or 

 brownish rhizomorphs. The formation 

 of the toadstools on the mycelium, which 

 in turn produce countless numbers of 

 spores, completes the round of life of 

 Armillaria mellea. 



From a large series of observations it 

 is concluded that the fungus is naturally 

 a saprophyte, but occasionally becomes 

 a semi-parasite, while under some condi- 

 tions evidently becomes a true parasite. 

 It is perhaps rightly termed a wound 

 parasite. Many times plants are injured 

 during cultivation. The wounds heal 

 slowly. Occasionally the fungus gains 

 an entrance before a wound has time to 

 close. Small roots sometimes die and 

 remain attached to the large one for a 

 time. The fungus grown in the decay- 

 ing roots finally comes in contact with 

 the live wood perhaps more or less weak- 

 ened by the presence of the decaying 

 wood with which it is in contact. The 

 fungus gradually encroaches on the live 

 wood, which slowly succumbs to the 

 action. The fungus thus becomes accus- 

 tomed to its surroundings and continues 

 to encroach more and more on the live 

 portion of the plant. While digging up 

 one small cherry tree, in which the crown 

 and main roots had been killed for a 

 distance of several inches, an observa- 

 tion was made which shows how this 

 fungus sometimes gains an entrance. 

 One of the main roots, although green 

 and apparently healthy for a distance of 

 about four feet, had a section in the cen- 

 ter, about six inches in length, which 

 was brown. An inspection of the 

 root revealed several small rhizomorphs 

 attached to the lower surface. A cross- 

 section of the root revealed an abun- 

 dance of the mycelium throughout the 

 bark and wood. The root of this cherry 

 tree had grown across a branch root of 

 some plant removed during clearing. 

 As the root decayed it became filled with 

 the fungus, which finally came in con- 

 tact with the live root of the cherry tree, 

 the result described. 



In the examination of a large number 

 of plants, both wild and cultivated, not 

 only a vast difiference in the injury to 

 dif¥erent kinds of plants, but to indi- 

 viduals of the same species was evident. 



Two or more fruit trees, apparently 

 killed by the same species of fungus as 

 indicated by the presence of the rhizo- 

 morphs, would show marked differences. 

 Some with numerous rhizomorphs grow- 

 ing into them, with many of the roots 

 dead and a portion of the crown badly 

 decayed, lived and matured an average 

 crop of fruit. 



In one instance a tree laden with a 

 splendid crop of mature, well colored 

 apples broke off at the crown during a 

 slight gust of wind. In another case a 

 large King apple failed to mature its fine 

 load of fruit. An inspection of the roots 

 and trunk revealed several rhizomorphs 

 clinging to the surface of the perfectly 

 green and' sound roots. Low on the 

 crown of this tree a few fissures, such 

 as would naturally occur on a tree of the 

 age of this one, had formed. The cam- 

 bium layer and neighboring bark and 

 wood, in many places, were completely 

 filled with dense layers of mycelium, 

 which could be easily removed to show 

 their connection and relation with the 

 rhizomorphs occurring on the roots. 

 The fungus had entered through the 

 small fissures in several places in the 

 trunk of the tree, gradually encroached 

 on the surrounding tissues, finally injur- 

 ing the tree to such a degree that it 

 could not mature its fruit. The tree, 

 other than failing to produce fruit and 

 lacking the usual abundance of foliage of 

 so large a tree, manifested no marked 

 injury. 



Another interesting observation was 

 made while examining a cherry tree of 

 some seven or eight years of age that 

 would not respond to an application of 

 barnj'ard manure, irrigation and good 

 cultivation. In examining the trunk of 

 the tree no rhizomorphs could be seen, 

 nor was there the slightest discoloration 

 of the trunk and large roots, as far as 

 could be determined without threatening 

 the life of the tree. By an accident it 

 was later discovered that some of the 

 roots had been cut while cultivating 

 raspberry plants, which were also grown 

 in this field. By examining the roots at 

 a distance of several feet from the trunk 

 of the tree several of them were found 

 to be dead and in condition of decay. 

 Every one of them contained rhizo- 

 morphs, which could be traced along and 

 through the roots for a distance of sev- 

 eral inches. Every root gave evidence 



Figure 3 — Showing a portion of the root and 

 stem of young red raspberry plant killed by 

 Armillaria mellea. The root shows many 

 rhizomarphs attached to it. Three toad- 

 stools occur on the stem. These toadstools 

 are the fruiting stage of the rhizomorphs. 



that the fungus was slowly encroaching 

 on the partially green wood. 



In the examination of many dead or 

 dying blackberry and raspberry plants 

 very similar conditions to those described 

 above were found to exist. Commonly 

 the crowns of diseased plants were well 

 filled with the rhizomorphs. Very fre- 

 quently many of the roots were also 

 badli' infested. It was not a rare occur- 

 rence to examine plants on which the 

 crown, though dead, had many roots that 

 were yet green and apparently healthy 

 a few inches remote from the crown. 



In the case of such plants as fruit trees, 

 which are grown some distance apart, 

 only a few scattering trees in an orchard 

 show signs of injury. In the case of 

 bush fruits and other plants grown 

 closely together the neighboring plants 

 are usually affected. Rarely do single 

 hills die or even show signs of injury 

 without the neighboring one becoming 

 infested. Usually one or more plants 

 become infested, and from such places 

 the disease spreads to neighboring plants, 

 which later succumb. In some instances, 

 but of rare occurrence, large groups of 



Figure 1— SECTION OF ROOT OF BLACKBERRY PLANT, WITH NUMEROUS 

 RHIZOMORPH OF ARMILLARIA MELLEA ATTACHED 

 This root was killed by the fungus 



