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fallen off. These were dried and threshed out, so that any selective 
effect that might have come from the picking of individual burs 
was eliminated. — 
In May, 1905, before the opening of the rainy season, two lots 
of these seeds of 10,000 each were counted out and planted in 
two locations on the Mexican plateau near the town of Apam. 
The location was one where none of these plants were growing 
and was well isolated in an abandoned Maguay field. The grass 
and herbaceous vegetation were removed from one plot and a 
corresponding plot but a few feet distant was left untouched. The 
seeds were distributed irregularly but were well scattered over 
the two areas. Brush was dragged back and forth over the first 
area, mixing the seeds somewhat with the soil. After the onset of 
the rains in June, the area was visited when the seedlings were 
about two inches high and a census was made, showing 8,931 in 
the favorable plot and 44 in the normal plot. At the same time a 
search of the surrounding region for plants of this species showed 
none growing nearer than about 3 kilometers, so apparently all 
the seedlings in the area were from the seeds which I introduced. 
Late in June of 1905, two additiona! lots of 10,000 each were 
planted in a similar manner about 10 kilometers to the: west of 
Cuernavaca. These plots were not seen again till September when 
the plants had reached a considerable size and had been subjected 
to some grazing by burros. No plants of the species were found 
within 1—1/, kilometers of this location and then only sparingly, 
so that the growth on my two plots represented very largely if 
not entirely the result of the planting. The census made at this 
time showed in the favorable plot 9,117 plants, and in the normal 
plot, 3,046. The two plots were very uniform, so that the unmodified 
plot presented less difference from the first plot than in the other 
test. Late in September, well after the close of the rainy season, 
when no growth would take place untill the following year, two 
other lots of 10,000 each were planted in an isolated location about 
three miles to the south of the Hacienda of Tetlama. These seeds 
remained in the plots over the dry season, germinating in June, 
1906. The last week of June, 1906, a census was made, showing 
Genetica. 28 
