Laffeety and Pki'HYBRidge — On a Phytophthora Parasitic on Apples. -k\ 



VI. — Practical Considerations. 



There is no reason to snppose that this particular form of apple-rot is likely to 

 become a serious menace to fruit-growers in this country. It is not known how 

 or from what source the fruits became infected. In other cases of Phytophthora- 

 rot of apples, however, it has been observed that the affected fruit was confined to 

 the lower branches of the trees near the ground ; and it is believed that infection 

 came from the soil as a result of rain splashes, &c. In such cases judicious 

 propping up of the hanging branches would probably suffice to prevent infection. 

 In some cases, too, the rot lias been recorded as being particularly prevalent in 

 fallen apples ; but whether infection took place before or after falling is not clear. 



Seeing that Osterwalcler found P. Gactormn {omnivora) causing a die-back of 

 apple-shoots in Switzerland, a careful search was made amongst the trees in the 

 orchard at Pilltown, Co. Kilkenny, from which the Iiish apples came ; but no trace 

 of any such injury was to be found there. Further, an attempt made Lo infect apple 

 twigs through wounds in the bark with a pure culture of the Irish fungus was not 

 successful. 



Since oospores of the fungus are formed in the tissues of the rotted apples, it 

 is clear that such sources of re-infection for the following season should not be 

 allowed to remain in the orchard. From a general hygienic point of view, as well 

 as in regard to this particular fungus pest, all rotted fruit should be collected and 

 suitably destroyed. 



We desire to express our indebtedness to the persons named iu the text of this 

 paper who were good enough to furnish us with material for comparative study, 

 and also to Sir Frederick W. Moore, of the Eoyal Botanic Gardens, Grlasnevin, 

 who kindly placed at our disposal Cereus, Cactus, and other plants for inoculation 

 purposes. We also desire to record our indebtedness to the Imperial Bureau of 

 Mycology in Kew, and to Dr. H. M. Quanjer, Wageningen, for assistance in the 

 matter of literature. 



VII, — Summary. 



The present paper deals with a rot occurring in apples in Ireland which was 

 found to be caused by a species of Phytophthora which proved to be P. Syringae 

 Klebahn, and not P. Cactorum Schroet., a species that has been recorded several 

 times as the. cause of a similar rot in apples and pears in other countries. 



Tlie causative fungus was isolated and studied in detail, in pure culture. It 

 was found to produce both paragynous and amphigynous antheridia, but the latter 

 are formed in relatively quite small numbers. 



Pv.enewed studies of P. Cadorum Schroet. and P. Fagi Plartig revealed the 

 fact that in these species also amphigynous antheridia occasionally occur, though 

 they are much rarer than paragynous antheridia. 



Apart from those species in which the sexual organs are imperfectly known or 

 have not been discovered, P. JVicofianae de Haan is the only species of this genus 

 in which the antheridia, so far as is known at jDresent, are exclusively paragynous. 



It is suggested that renewed investigation of this species might lead to the 

 discovery of some medium on wliich its sexual organs would be developed in 

 abundance, and it is thought that amongst them examples with amphigynous 

 antheridia would possibly be found. There is also a possibility that some of the 

 species of Phytophthora which apparently have amphigynous antheridia only 

 may yet be found to produce paragynous antheridia occasionally. 



