376 



that aeciospores were produced on Bcrheris from infections from telio- 

 spores of I'ticcinia pocuJifonni.s from wlieat, and tluis definitely estab- 

 lished heteroecism in tlie Uredineae in 1804. He also showed that nredi- 

 niospores followed by teliospores were produced on wheat by sowing aecio- 

 spores from the barberry. DeBary's radical discovery was rather slow 

 in being accepted by many other botanists, yet his evidence was indis- 

 putable and his interpretation prevailed. 



Oersted, working independently and contemporaneously with DeBarry, 

 established similar alteration of spore forms on different hosts between 

 the genera Gi/innosjx/raiif/iiim on cedars and RocstcJia on the apple family. 



This was epoch-making work in this line and showed the necessity 

 for accurate observations and most careful cultures to show the definite 

 lelationships of the different aecial forms. This work was taken up by 

 liotani.^ts both in the old and new world and is still being carried on with 

 much success. Early workers in Europe, beside DeBary and Oersted, 

 were Fuckel. Magnus, Schi<)eter, Wolff, Rostrup, Winter, Nielson, Reich- 

 ardt, Ilartig, Kathay, roriui and I'lowrigJit. .M(He recent workers of the 

 did world are Fischer, Klclmlm, 'I'ranzschel, von 'I'liheur, Wagner, I'.ubak, 

 ,Iuel, Ilennings, Eriksson. Dietci, Llro and others. 



In America Farlow and Tha.xter did pioneer work, followed later, and 

 with greater success, in this line l)y Arthur, Kellerman, Clinton, Kern 

 and others. The work of I >r. J. C. Arthur stands out prominently above 

 all others. 



The methods used l>y the different workers are, in the main, very 

 similar, viz: germinable spores of one stage are placed on sterile phints 

 of the suspected alternate host. Conditions of heat and moisture being 

 kept as favorable as possible throughout. In the methods use<l I)y Dr. 

 .\rthur, the perfectly healthy potted plants are kept covered with bell- 

 Jars for three days after the spore sowing is made. Each day the bell- 

 jars are removed fen- five minutes or so to allow the entrance of a fresh 

 supply of air, after which they are sprinkled within and replaced over 

 the plants, and the plant thus covered is left in a shaded place until about 

 a day after the bell-jar is removed. The inoculated leaves are then kept 

 well moistened and kept out of too strong light and carefully watched 

 for spore develoi)ments. especially after the first week. If the culture is 

 successful the first spore structure will usually he evident in a week or 

 ten days, followed later by the second spore structure, when that is pres- 



