Laffeety and Pethybriijge — On a Phytophihora Parasitic on Apples. 35 



IV. — Previous Work on similar Types of Rot. 



During recent years several eases of Phytophthora attack on apples as well as 

 on pears have been recorded both in Europe and in America. Thus, Osterwalder^ 

 described one on apples in Switzerland in 1904; Marchal/ Bubak/ Unamuno,* and 

 Schoevers^ reported attacks on pears in Belginm. Bohemia, Asturia, and Holland 

 respectively at various times from 1908 to 1915; Whetzel and Eosenbaum" 

 recorded an attack on apples in America in 1916 ; Wormald' dealt with attacks on 

 pears and apples in England in 1919 ; Giissow** noted an attack on pears in Nova 

 Scotia in 1920, while in the same year Clinton" gave particulars of attacks on both 

 apples and pears in Connecticut, U.S.A. 



In all these instances the rot was attributed either to Phytofhtliora Cactonom 

 (Leb. et Cohn) Schrot. or to its synonym P. omnivora de Bary," but in no case was 

 any intensive study of the sexual organs of the fungus made, nor was the existence 

 of two kinds of antheridia suspected or discovered. 



At the outset it appeared possible that the rot in the Irish apples was caused 

 by a new species of Bhytophthora, because neither in P. Gaciorum nor in any 

 other species of Phytophthora hitherto described had the production of two kinds 

 of antheridia in one and the same species been noted. On the other hand, it was 

 not impossible that antheridia of the two types really did occur in P. Cactorum, 

 and perhaps in other species of the genus, but that the fact had merely been 

 overlooked or not apprehended by previous workers, owing to the comparative 

 scarcity of cases in which the antheridia are amphigynous as compared with those 

 in which they are paragynous. 



This latter surmise was strengthened as a result of a consideration of the 

 relevant literature. Thus, Hartig," in his description of the development of the 

 oospore in P. Fagi, states that in exceptional cases the stalk of the oogonium 

 swells out directly under the oogonium itself to form the antheridium, and his 

 figure of this condition (Taf. Ill, tig. 24b) suggests very strongly that this was 

 an instance in which the antheridium may have been amphigynous. Butler and 

 Kulkarni,'^ after referring to Hartig's figure and to the statement of Himmelbaur,*^ 

 that in P. Fagi the antheridium is attached to the underside of the oogonium near 

 its base, says : " It appears probable that a penetration of the antheridium by the 

 oogonial stalk sometimes occurs in this species." 



1 Centralb. f. Bakt., ii, xv, 1906, p. 4o5. 



2 Bull. Soo. Roy. de Belgique, xlv, 1908, p. 343. 



^ Zeitsohr. f. Plianzenkrankheiteii, 'Xx, 1910, p. 2o7. 



■•Zeitschr. f. Pflanzenkraiikheiten, xxi, 1911, p. 379 (abstract). 



"Tijdschr. over Planteiiziekteii, xxi, 1915, p. 153. 



^ Phytopathology, vi, 1916, p. 89. 



"Ann. App. Biology, vi, 1919, p. 89. 



8 Phytopathology, x, 1920, p. 60. 



» Couii. Agric. Expt. Station, Bull. 222, 1920, p. 406 and p. 454. 



'"It will be remeiubered that tie Bary in 1881 assembled Schenk's Fervnospord Sempermvi 

 and Hartig's Perunospora Fcuji under the new name Phytoj^hthora omnivora ; and, later in the 

 same year, also included Lebert and Oohn's Peronospura Cactorum, under the same name. 

 (Beitr. z. Morph. u. Phys. d. Pilze, iv, 1881, and Bot. Zeit., xxxix, 1881.) Himmelbaur, however, 

 has shown that P. Fagi and P. Cactorum are dissimilar (Jahrb. Hanib. Wiss. Anst., xxviii, 1910), 

 and for this reason as well as on priority grounds the combination P. omiikora should no longer 

 be used. 



" Unter.'iuch. forstbot. Inst. Miinchen, i, 1880, p. 49. 



■-Mem. Dept. Agric, India, Bot. Series, v, 1913, p. 257. 



'^ Jahrb. Hamburg Wissensch. Anstalten, xxviii, 1910, p. 450. 



