238 PHYTOPATHOLOGY [VOL. 6 



tree and of the group of trees of which it is a part. In one of the examples 

 given in the introduction to this paper, only five galls out of a total of 

 173 were over five feet from the ground. In another case only about 

 twenty out of 529 were found above six feet from the ground. Often 

 they are found only on one side of the tree or the group, unevenly dis- 

 tributed. Since we must assume that at the time of spore dissemination 

 all the young twigs and branches are equally susceptible to infection, a 

 shower of spores would find equal conditions for germination and pene- 

 tration of the bark, at least in a majority of twigs or branches, and the 

 infections would be more evenly distributed over the crown. The fact 

 that in our experiments inoculation with wounding was successful in 

 five out of seven cases and gave only one very doubtful result in the 

 unwounded tree which subsequently died, speaks for the intervention 

 of insects in nature. 



All other causes of wounds through which infection could take place 

 are absent in the case of Pinus radiata and P. attenuata. The winters 

 of their habitat are very mild; the summers too cool for sun-scorch. Light- 

 ning and hail are practically unknown. 



The common occurrence of spittle-bugs (Aphrophora sp.) on young 

 stems and twigs of Pinus radiata may have some significance. During 

 spring, that is, at the very time when the galls of Peridermium harknessii 

 are in full sporulation, the writer found them profusely .at Monterey, 

 California, throughout the very heavily infected stands. The larvae 

 of this cercopid wound the young stem by puncturing it. Provided the 

 spittle contains no ingredients harmful to the aeciospores caught in it, 

 the latter would find ideal conditions for germination by being kept moist 

 for a considerable time. When the spittle dries up they would auto- 

 matically be drawn onto the fresh wound made by the insect. It is to 

 be noted that the spittle-bugs are nearly always located on young stems 

 and twigs which are still protected by needles. The writer's inoculations 

 show that not only the youngest stems, but also at least three-years-old 

 ones may be artificially infected. In nature this is rare; so are spittle- 

 bugs on three-years-old stems. 



Hedgcock and Long 22 find that the swellings of Peridermium fusiforme 

 "on the three-needle pines often originate near the extremity of a branch, 

 and, as the side branches develop, the fungus invades them, producing 

 an enlargement of the base of each branch." Pinus radiata is a three- 

 needle pine and similar enlargements of the base of each branch of a whorl 

 are not uncommon. Spittle-bugs very often are located on the whorl 

 at the base of the branches. 



22 Jour. Agr. Res. 2: 248. 



