IOWA ACADEMY OF SCIENCES. 
163 
Roestelia. It is found on the apple and allied plants belonging 
to the tribe Pomese, of the family Rosacese. 
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. 
Gymnosporangium macropus, Lk., the particalar species 
under consideration, is confined exclusively to the Red cedar, 
Juniperus Virginiana, L. Its Roestelia form is known as 
Roestelia pirata, Thax. , and is found on cultivated apple {Pirus 
malus, 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 following spring these balls enlarge and during rainy 
weather put out several orange -colored gelatinous horns. 
At this time the bails 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 a.nd with tooth like projections beneath. Within the pro- 
jections are formed round one-celied spores (aecidiospores) 
which may be carried to a cedar where they will germinate 
and repeat the life cycle. 
The connection of Gymnosporangium macropus with Roestelia 
pirata has been established beyond question by Dr. 
Thaxterh The inoculation experiments here reported were 
not u Oder taken for the purpose of obtaining 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 free 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 
iQu certain cultures of Gymnosporangium with notes on their Boesteliae. Am. Acad. 
Arts and Sciences, 1886, p. 259. 
