IOWA ACADEMY OP SCIENCES. 163 



Roestelia. It is found on the apple and allied plants belonging 

 to the tribe Pomega, of the family Rosaceso. 



In the United States there are nine species of Gymnosporan- 

 gium. Chiefly through the investigations of Doctors Farlow 

 and Thaxter, all of them have been connected with their cor- 

 responding species of Roestelia. 



Gymnospomngium macropus, Lk., the particular species 

 under consideration, is confined exclusively to the Red cedar, 

 Juniperus Virginiana, L. Its Roestelia form is known as 

 RcesteUa pirata, Tnax. , and is found on cultivated apple {Pints 

 mains, L.), wild crab (Pirus coronaria, L.) and Juneberry 

 {Amelanchier). The Gymnosporangium may be found in the 

 autumn upon the twigs of Red cedar, where it appears in the 

 form of small brown balls about the size of peas. In May of 

 the foliowiiDg spring these balls enlarge and during rainy 

 weather put out siveral orange-colored gelatinous horns. 

 At this time the balls are very conspicuous objects and are uni- 

 versally known as ' 'Cedar apples. " The gelatinous horns contain 

 numerous two-celled spores on long pedicels. The spores 

 germinate in situ each one producing several minute secondary 

 spores which are readily carried by the wind. When these 

 secondary spores chance to fall upon leaves of apples or other 

 suitable plant, they germinate and enter the tissues. In about 

 three weeks, small yellow spots appear on the upper surface of 

 the apple leaf. This is the Roestelia, and when it is mature 

 the spots will be one-fourth to one-half inch in diameter, yellow 

 above and with tooth like projections beneath. Within the pro- 

 jections are formed round one-celled spores (secidicspores) 

 which may be carried to a cedar where they will germinate 

 and repeat the life cycle. 



The connection of Gymnosporangium macropus with Eoestelia 

 pirata has been establisaed beyond question by Dr. 

 Thaxter^ The inoculation experiments here reported were 

 not undertaken for the purpose of obtainicg further informa- 

 tion concerning the relationship existing between the two 

 forms of the fungus, but rather to ascertain why the cultivated 

 apple in central Iowa should be iree from Roestelia. Although 

 the field has been thoroughly canvassed nearly every season 

 during the past twenty-five years, no species of Roestelia has 

 ever been taken on any variety of cultivated apple in the 



lOn certain cultures of Gymnosporangium with notes on their RocstcUac. Am. Acad. 

 Arts and Sciences, 1886, p. 359. 



