BULLETIN 360, U. S. DEPARTMENT OF AGRICULTURE. 



TABLE III.. Inoculation of Razoumofskya campylopoda on Pinus ponderosa, 

 made in November, 1911. 



[x= Inoculation effective; 0= inoculation not effective.] 



A study of Table III shows that the branches were infected in 

 three out of the five test cases on the youngest and last internode on 

 which the seeds were placed. Infection occurred on two of the five 

 tested branches on that part 1 year old at the time of sowing, one 

 infection only being on the 2-year-old portion. Infection did not 

 take place on the older parts of the branches. A tree never be- 

 comes too old for infection to occur on its youngest branches. Sup- 

 pressed trees may escape, owing to the fact that slowness of growth 

 and more rapid formation of thick bark lessens the chance of infec- 

 tion; also shortness of twig growth gives less opportunity. The 

 demand for a fair amount of light is also a factor in such a case, 

 not, however, for the stages of germination and penetration of the 

 primary root, but for the subsequent development of the aerial parts. 

 Mature trees becoming infected on tender branches may not suffer 

 any appreciable injury, but in time the decline of the tree is surely 

 hastened, since the gradually increasing hypertrophy of the branches, 

 the breakages, and the thinning out of the foliage of the tree as a 

 whole cause it to be greatly weakened. Almost always the result of 

 a heavy infection on the trunk and branches of some conifers is the 

 death of the upper portion of the crown, 1 causing staghead (fig. 6), 



1 The dying back of the crown of trees, commonly known as spikctop, or staghead, is 

 attributed to various causes ; as many, in fact, as the varied conditions under which trees 

 grow. One of the most common theories is that on opening up a stand the admission of 

 light to the trunk and lower crown deflects the transpiration current to the older branch 

 orders or, as with some species, promotes the formation of a secondary crown on the 

 main trunk. This stimulated foliar activity below reduces the water supply at the top 

 of the crown ; consequently the topmost branches die back. This is exactly what happens 

 in the case of mistletoes. The extra crown development below, by brooming, starves out 

 the crown above, resulting in its death. Miinch (Silva, December, 1911, pp. 415-416) 

 claims to have found a parasitic Ascomycete which causes staghead in the oak of Europe 

 by attacking the bark and outer wood of the main shoots. The writer has found a 

 wood-destroying fungus which attacks the upper crown branches of the chestnut in 

 southern Indiana and causes their death. The " pencil rot," which seems to be fre- 

 quently the cause of staghead in the western red cedar, is another example of fungi at- 

 tacking the crown of trees. Lightning is a common cause of staghead ; also injury by 

 insects. 



