Laffkim'y and Peihybkidge — On a Phytophthora Parasitic on A])ples. 39 



one' published in Llie following year, the various species of Phytophthoia which 

 had been described up to that time (nuniberhig fourteen, or possibly fifteen) were 

 eniuuerated. Since then the following seven species have been recorded ; — 



P. fid Eau° P. terrestria Sherb."' 



P. citri Eau- P. Meadii McEae'* 



P. Aim Saw.-' P. cvyptogca Pethyb. and Laff.° 



P. Mdongcnac Saw." 

 — whilst what may possibly turn out to be three new species have been reported 

 as attacking Paeony, Ehnbarb, and Oats respectively in the United Slates of 

 America,' and another unidentified species has been found by Brittlebauk, causing 

 a disease of Pcqmver nudiccmle, in Australia.^ Thus, there would now appear to 

 be some twenty-two species ; but further study of them will probably result in a 

 slight reduction of this number, since some of them, like P. 'lluobromae and 

 P. Faberi, /'. parasitica and P. terrestria, P. Nicotianae and P. jatrophac, are 

 probably identical.^ 



When amphigyny was first discovered, it was proposed that the genus 

 Phytophthora slioidd be divided into two. The generic name Phytophthora 

 was to be retained only for those species with amphigynous antheridia, with 

 P. infestans as type ; while those in which the antheridia are lateral were to be 

 placed in a genus for which the name ISTozemia was suggested, with N. Cactorum 

 as type, it being assumed, of course, that in a given species only one and the same 

 type of antheridium would be present. The Cactorum group then included 

 Nozcmia Cactorum, N. Fagi, N. Syringac, and N. Nicotianae. But it is clear from 

 the work described in the present paper that the first three of these species 

 cannot well remain in it. Having both amphigynous and paragynous antheridia, 

 they constitute an intermediate group linking Phytophthora with Nozemia. 



On the removal of these three species the sole representative of the latter 

 genus would now be N. Nicotianae. It is true that de Haan's description and 

 illustraiions of the morphology of the sexual organs in this species clearly show 

 that the antheridia are paragynous ; nevertheless, in view of the discovery of cases 

 of amphigyny in the other three species, it seems not at all improbable that 

 examples of this condition might be found to occur also in N. Nicotianae ; and 

 further investigations on this species are highly desirable. For pure culture work, 

 however, no medium has yet been found on which this species produces its sexual 

 organs with certainty or in abundance ; and the point cannot therefore at the 

 moment be cleared up. Furthermore, renewed investigations directed to this 

 special end might eventually show, as regards those Phytophthoras in which the 

 antheridia are, so far as is known at present, amphigynous, that these organs may 

 occasionally be paragynous. 



In view of these and other considerations arrived at as a result of more 

 exlended research, it is now thought better that the recently erected genus 



1 Jouri). Econ. Biol., ix, No. 2, 1914, p. 53. ^ Jouru. Bombay Nat. Hist. See. xxiv, p. 615. 



3 Mycologia, ix, No. 4, 1917, p. 249. * Phytopathology, vii, No. 2, 1017, p. 119. 



° Mem. bept. Agric. India Bot., Series ix, No. 5, 1918, p. 219. 



° Sci. Pi-oc. Roy. Dublin Soc, xv (N.S.), No. 35, 1919, p. 487. It is of interest to note 

 that when this species was described its sexual organs were known only from pure cultures. 

 Since that time, however, the authors have found them in the decayed tissues of the host 

 plant. 



' Science,N.S.,liv,1921. p. 170; Phytopathology, xi, 1921, p. 55; and Science xliii,191C, p.534. 



* Journ. Dept. Agric. Victoria, xvii, Pt. 2, 1919, p. 700. 



" While the present paper was in the press a reference to A&hby's P. palmicora was noted. 

 We have not yet seen the paper in which it is described. (West Indian Bull., xviii, No. 1 

 1920, p. 61.) 



