1904] BRIEFER ARTICLES 65 
ing aecidia. The weeds were over two feet high, mostly Ambrosia trifida, 
with many small plants of other species beneath, the Oxalis being abundant. 
As this aecidium is rarely collected, I began to gather herbarium specimens, 
and observed that while nearly every leaf on the lower half of the Oxalis 
stems was infected with the rust over an area of about three feet in diameter, 
beyond that area it grew less frequent, and was quite absent in four or 
five feet from the center of the infected area, although the Oxalis plants 
were equally abundant everywhere in the vicinity. It seemed to me this 
gave evidence that the teleutosporic source of infection was within the 
narrow limits of the rusted area. I reasoned that if the sporidia had been 
blown from a distance, the infection would have been more evenly distributed, 
and over a larger area. _I observed that the lowest leaves on the plants 
were most thickly dotted with aecidia, and especially those caught beneath 
the tangle of dead stems from last year’s growth. This indicated that the 
germinating teleutospores must have lain close to or upon the ground, and 
that the protecting weeds and shrubs had prevented currents of air from 
materially distributing the sporidia. 
I now instituted a search for remains of sedge or grass which might 
happily show a few teleutosporic sori. Usually one is embarrassed by 
finding portions of many species, often unidentifiable, but in this case I 
could find no clumps or stalks of sedge or grass within the infected area, 
apparently none having grown the previous season, doubtless prevented 
by the dense thicket of tall weeds, or else they had wholly disintegrated. 
There was, however, quite a mass of débris deposited by the spring over- 
flow of the near-by river, made up largely of broken cornstalks, but so 
covered with silt that it was impossible to tell if they had borne rust or not. 
The cornstalks did not occur beyond the affected area, and so were seized 
upon as a possible, although very dubious, clue. 
The task of testing this inference was neither difficult nor protracted, 
a piece of good fortune but rarely encountered. Rusted leaves of the 
Oxalis were taken to the laboratory, about two miles distant, their long 
Petioles placed in a vial of water, and adjusted over a potted plant of corn 
(Zea Mays L.), the whole being covered with a bell jar. On the third day 
the bell jar was removed. 
On the fifth day the corn leaves appeared paler where the spores had 
Presumably fallen; on the seventh day watery pimples began to show; and 
on the eighth day a few uredosori had opened. In a day or two more 
hundreds of characteristic sori were displaying a wealth of fuscous spores; 
and nearly the whole green area of the leaf blades, upon both sides, was so 
thoroughly rusted as to threaten the life of the tissues. 
