Microscopical Anatomy of the Common 
Cedar- Apple (Gymnosporangium Macropus ). 1 
BY 
ELMER SANFORD. 
With Plate XIII. 
^TMIIS species of cedar-apple originates in the leaves of the 
JL smaller branches of Juniperus virginiana. The my- 
celium of the fungus causes an abnormal growth in the leaf 
tissue, which carries up the apex of the leaf as it develops, 
and pushes the branch to one side until the knot itself appears 
to be terminal. The growth thus produced varies from about 
a twelfth of an inch to an inch and a half in diameter, and 
finally becomes reniform from the cells of the outer part of 
the knot multiplying more rapidly than those at the base. 
The knots are of a silvery-gray colour. About the first of 
May, after the knots have remained over winter, the myce- 
lium of the fungus collects in masses a little beneath the 
surface, raising it up into little papillae, varying in number 
according to the size of the knot, but usually appearing over 
the surface about an eighth of an inch apart. Later, the 
surface of the knot is broken through at these points, and 
yellow cylindrical masses, composed of spores borne upon 
long hyaline and more or less gelatinous stalks, are pro- 
truded, and, when moist, swell up, and often extend to the 
length of nearly an inch. Figure i is a drawing of one of 
these cedar-apples as it appeared the twelfth of May ; a the 
branch on which it is borne, b the body of the apple, c one 
of the spore-masses, and d the ring at the base of the spore- 
1 This study was carried on in the Botanical Laboratory of the University of 
Michigan in May and June, 1887, under the direction of Professor V. M. Spalding. 
[Annals of Botany, Vol. I. Nos. Ill and IV. February 1888.] 
