

270 



the host plant. Conidial forms as a rule are rampant parasites, 

 whereas the primitive or sexual stage of the same fungus is 

 usually a saprophyte, and only appears when the host is on the 

 wane, if not quite dead. 



The members of the Peronosporeae illustrate the gradual 

 transition of a primitive group of fungi from an aquatic to an 

 aerial habitat. The sexual and oldest stage of the fungus as yet 

 retains so much of its original nature that the reproductive bodies 

 take the form of zoospores, whose only mode of dissemination is 

 by means of water, which obviously limits their dispersion on 

 land. By the addition, however, of a conidial stage, whose repro- 

 ductive bodies are dispersed by wind, animals, insects, &c, the 

 various members of the Peronosporeae have been enabled to 

 extend the area of their distribution to the utmost limits of 

 range of the hosts to which they have become adapted. 



The parasite which causes the disease about to be considered 

 presumably belongs to the category of " form-species," but as yet 

 there is no direct evidence on the point, since pure cultures of 

 the comdia have hitherto failed to produce any other form of 



fruit. 



Naemosp 



more 



v. +v7 — -u ^^».«w»k;(*o, wuiuu i» uuaracterisea 



by the absence of a definite perithecium or fruit enclosing tne 

 reproductive bodies or conidia. 



During the past few years numerous inquiries have been 

 addressed to Kew respecting the disease, aptly termed by one 

 correspondent as " die-back of two-year-old peach shoots." 



In the spring the leaf-buds expand normally, without any 

 suggestion of disease, but just about the time when the blossom is 

 v . e *? and f d t} l e y° ull g leaves suddenly wilt, turn brown, and 

 ™«Vir ln a 7 dayS - At the same time the Petals change to a 

 fhf LI°T n r l0UI ' and the flowers dro °P> b *t remain attached to 

 lw« hi f • for r me J 1 ? 6 ' as also do the leaves. Finally the 

 ™i ™in« S ****** leaves and flowers assam e a deep claret- 

 red colour, and shrivel more or less as the season advances. 



terS?o^ V ?if re v he distin ? ive and unvarying naked-eye charae- 

 when th. ,w, d i 1SeaSe Under consideration. About midsummer, 

 Ind ran% dead + l ea 7f S and powers have been removed by wind 

 bv thTor . IZL £ haVe been badly di8eased ™* °e recognised 

 two feeUn Wth n £ mero ™ «** ^oots, varying from one to 

 folIowL VZ n>' V nl i g the months of M ay and June of the 

 be found tot t^ dea ? branches ' if carefull y examined, will 

 orange-colour^ T'S -fi? 88 t^^ budded with minute, dull- 



«pores e 5? ELESS** "' C ° nSiSting ° f myriad8 ° f 



tendriWitobrSv*? ^ t + hr °?- gh a branch at fche P° int wfa ere such a 



of a mor?^LpS r0trU i dm l' the fungUS wi » be seen to consist 

 spheres which LI r-? ed 8phere situated ™ the cortex. These 

 sol d ma Ts b f mJK 1 * 6 n » me ™s, consist at first of a minute, 



becomeT hollow ^fr;/ 1 ! 10 ^^^ 11 ^ increa8es in size ' 

 slender threads 'or snoronhT ^'K ^ With elosely-packed, 

 forming the inside 5, fr 9 ' ? hlch ori S 5 ™te from the cells 



ing into thVwv tVSli J he .f. phere » With ^eir free tips project- 

 tf cavity of the fruiting body. The minute spores are 



