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IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
waxy appearance when emptied of aeciospores. The peridial 
wall is not recurve as in white and red clover rust but more 
flask shaped. See figure 90; figure 92 (1, 2, 3) ; Plate XV, A; 
Plate XVI, A. 
Aeciospores- — Shape — Globose, subglobose, to ellipsoid-angular ; 
wall color, starchy white, less than 1 Mu. thick; surface mi- 
nutely verrueose; sizes 10-22x15-26 Mu.; standard 17-20x20-24 
Mu. (54 measured) ; germination, Minimum, 4° C., Optimum, 
14° C., Maximum, 22° C. The first spores emitted from an 
aecium are more viable, more active and have a quicker pene- 
Fig. 91. — Tracing from a camera lucida drawing. 1, Teliospore of Alsike 
Clover rust germinating: Spore collected October 31, 1916. Set to germinate 
December 19, 1916. . Drawn December 22, 1916. Spore 20.4x27.2 Mu'. Pro- 
mycelium 6.8x170 Mu. Sterigmata 2x4 Mu. (average). S'poridia 14x17 Mu. 
(average). 2, A sporidium of 1 germinating while on the sterigma. Germ 
tube 3.4x34 Mu. long. 3, An average sized sporidium 7x14 Mu. 
tration than later ones. These aecia differ in that about twenty- 
four hours after opening, the spores seem mostly lifeless. The 
most successful time to inoculate with these spores is just as 
they come from the aecial cup. Viability one to three hours. 
Period of noted infection nine to fourteen days. See figure 90. 
The following tables show the relative measurements of spores 
and peridial cells from the rusts on three clovers. All measure- 
ments are in microns, the width being first indicated. 
