230 PHYTOPATHOLOGY [VOL. 6 



Strong as are the reasons for assuming that Peridermium harknessii 

 is identical with Peridermium cerebrum, there are well-founded considera- 

 tions which make it imperative that the connection should actually be 

 proved by inoculation. One of these is the apparent independence of 

 Cronartium Quercuum and Peridermium harknessii. Another is the dif- 

 ference in appearance. The aecia of Peridermium harknessii, at least 

 on Pinus radiata, are not typically cerebroid (fig. 2) ; they usually appear 

 as separate sori and the rather delicate peridium breaks open very soon 

 after coming up through the bark. A comparison of figure 2 and Hedg- 

 cock and Long's photographs (their plate XI) show the difference very 

 plainly. More important is the apparent rarity in our Peridermium of 

 pycnia exuding "abundantly a yellowish, sweet fluid" as on Peridermium 

 cerebrum,* which are also mentioned by Shear. 10 In spite of diligent 

 search the writer has only once succeeded in finding pycnia of Peridermium 

 harknessii on a young gall on Pinus jeffreyi in early spring (April) . The 

 pycnia contained very small pycnospores and did not break through the 

 bark. In the literature the writer does not find any other reference to 

 pycnia on Peridermium harknessii. To these distinctions may be added 

 the fact that in infections with Peridermium harknessii, particularly on 

 Pinus radiata, P. contorta and P. attenuata, witches'-brooms are extremely 

 common and that the galls very often continue to fruit for many years, 

 both of which phenomena are rare in Peridermium cerebrum according 

 to Hedgcock. 11 It is well to remember also, that all the numerous and 

 careful attempts at infection of Quercus agrifolia with aeciospores of 

 Peridermium harknessii have failed. 



The typically spindle-shaped form (Peridermium fusiforme) which 

 has recently been proved by Arthur and Kern 12 and by Hedgcock and 

 Long (I.e.) to be identical with Peridermium cerebrum, apparently 

 does not exist on the Pacific Coast or at least is very rare. The typical 

 gall of Peridermium harknessii is always very well defined; the transition 

 from stem to gall is never gradual, but always very abrupt. When the 

 infection takes place in 1- and 2-years-old twigs, the swelling generally 

 embraces the whole stem ; in the next year these galls often take the shape 

 of a pear, with the thick part downwards, and later become spherical. 

 On a little older stems the swelling may be one-sided and later develop 

 into a hemisphere. But whatever form the gall takes, it is always very 

 clearly set off against the un thickened stem; this is particularly noticeable 



9 Mycologia 4: 132. 



10 Jour. Myc. 12: 91. 



11 Mycologia 4: 143. 



52 Arthur, J. C. and Kern, F. D. North American species of Peridermium on 

 pine. Mycologia 6: 135. 1914. 



