40 PEACH LEAF CURL: TTR NATURE AND TREATMENT. 



reminds one of the sterio-mata bearing- the sporangia of Plujtojtlitlioi'n 

 h\f\xtan^. 



Thus far efforts to induce filamentous germination of the budconidia 

 or of the aseospores of Exoascvs deformaw^ in culture media have 

 proved unsuccessful. Brefeld has worked with this problem for 

 months, and the writer has frequently attempted to obtain this form 

 of germination.' Budding occurs, as already indicated, quite readily 

 in various nutrient solutions, and short promycelia from the aseospores 

 have been found in some cultures. In nearly if not all cases, however, 

 the aseospores showing promycelia or short mj^celial germination have 

 shown that this germination occurred under natural conditions upon 

 the peach leaf, the germinated spores being transferred from the leaf 

 to the culture in preparing the latter. It may be added here that the 

 bud conidia are also formed in vast numbers upon the surface of the 

 infested leaf aftei- the maturing of the aseospores. It is largely these 

 conidia which give the infested leaf the marked white appearance 

 commonly observed at the height of the disease. The leaf appears as 

 if covered with flour or a heavy white bloom. 



RELATIONS OF THE FUNGUS TO THE HOST. 



Under a previous heading in this chapter the physical conditions 

 which influence the serious development of peach leaf curl have ])een 

 considered in accordance with the light which we now have relative to 

 such influences, and there remain to be taken up at this time the more 

 intimate and direct relations of the host and parasite. These relations 

 include the action of the fungus upon the cell contents, the cell walls, 

 and the cellular tissues of the host; the probable mode of infection and 

 the spread of the parasite within the tissues; the wintering of the 

 fungus upon the tree; etc. 



'A very considerable number of cultural experiments liave been tried. The cul- 

 tures of aseospores and conidia have been subjected to temperatures innch below the 

 freezing point and to various degrees of heat in the thermostat. Sudden changes of 

 temperature have lieen tried. Increased and diminished amounts of oxygen, as con- 

 trasted with that of the normal atmosphere, have been tested. Even a chamber filled 

 with nearly pure oxygen has produced no apparent effect. Water from various 

 sources, such as rain water, dew, ice water, distilled water, tap water, etc. , has been 

 tested. Solutions of the various sugars, malt extract, sterilized beer, plum extract, 

 etc., were tried. Hanging drop cultures of various nutrient media and plate cultures 

 of potato-peptone-sugar gelatin have not shown germination. Drops of variou-s 

 nutrient solutions placed upon newly forming leaves dissected from unopened peacli 

 buds and these held in moist chambers have given only negative results. The same 

 is true for peach pits brought near to germination and the cotyledons treated with a 

 weak solution of diastase, the spores placed l)etween them and held at various tem- 

 peratures in moist chambers. Sections of such cotyledons with spores placed upon 

 them were also prepared in moist chambers. A brief treatment of the spores with 

 ether was tested without bringing about germination. 



Prillieux states that attempts to artificially infect the leaves or shoots have not 

 thus far succeeded (Mai. d. Plantes Agr., Vol. I, p. 399). 



