490 THE FUNGI WHICH CAUSE PLANT DISEASE 



An unidentified species has been reported on watermelon '* as 

 cause of considerable injury. Halstead mentions also an undeter- 

 mined species on oats.^' Pycnidia 150-250 fi; spores 12-18 x 

 6-7 /I, pyriform. 



Phoma (Fries) Desmaziere (p. 481) 



The genus as at present recorded contains over 1200 forms. 

 It is indistinguishable from Phyllosticta (see p. 484) except that 

 it is caulivorous. Several species are regarded as conidial forms 

 of Diaporthe, Mycosphserella, etc. 



P. reniformis on grape =Guignardia bidwellii. See p. 238. 



P. albicans Rob. & Desm. on chicory =Pleospora albicans. 

 See p. 260. 



P. betae Fr. on beet =Mycosphaerella tabifica. See p. 247. 



P. bohemica Bub. & Kab. on fir tree needles =Rehmielliopsis. 

 See p. 276. 



P. ambigua (Nitz.) Sacc. on pear = Diaporthe ambigua. See 

 p. 279. 



P. sarmentella Sacc. on hop =Diaporthe sarmentella. See 

 p. 279. 



P. persicae Sacc. 



Pycnidia scattered to gregarious, globose lenticular, ^/o-^/b nun. ; 

 conidia oblong ovoid, 8-3 x 2 n, conidiophores cylindro-conical, 

 equal in length. 



It produces constriction and death of peach twigs.^' 



P.maliS.&S.^'Ss 



Pycnidia gregarious, subcuticular, depressed, ostiole erimipent; 

 conidia oblong-f usoid, 2-3 x 5-8 fi. 



It attacks the wood of young apple trees and also causes a decay 

 of the fruit. 



P. cydonise Sacc." 



Pycnidia subgregarious, depressed, ostiole obtuse or erumpent, 

 conidia elliptic oblong, 8-9 /i long; conidiophores short. 



A form causing rot of quince fruit was provisionally referred 

 to this species by Halsted. 



P. limonis Thftm. & Boll. P. citri Sacc. and P. aurantiorum 

 (Rab.) Sacc. occur on citrous fruits; 



