411 



Note on the Life History of the Ertstphaceje. 



By Ernest S. Salmon, F.L.S. 



{Read May ISth, 1900.) 



Although this group of fungi, on account of the attacks of 

 some of its members (e.g. the Yine Mildew, the Hop Mildew, etc.) 

 on plants of great economic importance, is more or less well known, 

 two very important points in connection with the life-history 

 still require invesiigation. 



With regard to the fresh appearance of the mildew each year, 

 the question naturally presents itself — in what way and under 

 what conditions do the ascospores give rise every spring to the 

 conidial or Oidium stage ? — how do the ascospores get conveyed 

 from the rotting perithecia on the dead leaves or humus to fresh 

 host-plants, — the latter sometimes trees of a considerable height ? 



The life-history of the Erysiphacece is invariably described as 

 consisting of two regularly alternating phases of growth, — a for- 

 mation during the summer of conidia, and in the autumn of 

 ascospores with the function of giving rise after hibernation to 

 the conidial form again in the spring of the following year. It 

 should be remembered, however, that in the Erysijyhacece no direct 

 proof of this regular alternation exists. Although in a few cases 

 ascospores sown in a hanging drop of water have been observed to 

 develop short germinating tubes, yet all attempts to infect host 

 plants with ascospores have failed. 



The suggestion may be made that perhaps in some, or even 

 many, cases the conidia have acquired the power of hibernation ; 

 and to explain the occurrence year after year of the Yine Mildew 

 in England, — although the perithecial stage has never been 

 observed — some such assumption seems almost necessary. The 

 objection that the conidia, on account of their thin walls, would 

 be incapable of withstanding exposure to the cUmatic conditions- 

 of winter is unable to be maintained when it is remembered that 



