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Africa Seminars International and Christopher J. Schuberth, 
Geologist, and Curator of Education, The I llinois State Museum, 
present the 10th Annual \ y 
EAST AFRICAN GEOLOGIC SAFARI 
August 4-21,1981 
Olduvai Gorge . . . Kilimanjaro . . . Mombasa 
famed place names in Tanzania and Kenya. 
Tanzanite . . Rift Valley . . . Zinjanthropus . . 
are equally well known to science. 
A once-in-a-lifetime 2,000-mile educa- 
tional holiday adventure in a magnifi- 
cent land where lion is king, the 
giraffe is curious about you, . 
their homes in the Serengeti, 
Ngorongoro, Amboseli, or 
Tsavo will become as familiar 
to you as they are to them. Best 
of all, you travel in the company 
of thoroughly experienced, know- 
ledgeable, and dedicated leadership.^ 
For a detailed brochure or further 
information, call or write: 
Christopher J. Schuberth 
Africa Seminars 
1841 Broadway 
New York, N.Y. 10023 
Phone: (212) 765-4870 
and compared the average index of 
parent and offspring to distinguish the 
effects of gene flow. 
As expected, adult plants on the 
mine side of the first transect, running 
crosswind, are quite tolerant, with an 
index of six. The seedlings they pro- 
duce have a considerably lower tol- 
erance of about four. The difference 
in the tolerances of the adults and 
their seedlings provides a measure of 
the movement of nontolerant genes 
onto the mine soils. As McNeilly sam- 
pled closer and closer to the boundary 
between the mine and the pasture, 
the tolerance of both adults and off- 
spring gradually dropped, to about 
four and three, respectively. About 
sixty-five feet into the pasture, Agros- 
tis seedlings had a tolerance index 
of just over one — identical to that of 
the parent plants and close to that 
of completely nontolerant Agrostis. 
The second transect presented a 
very different picture. Close to the 
boundary on the mine side, tolerance 
among adults was high, at five. The 
tolerance of the seedlings of these 
plants was only a single index point 
lower, possibly indicating the slight 
effects of pasture pollen from the up- 
wind side of the mine. Surprisingly, 
this situation remained the same for 
more than 165 feet downwind into the 
pasture. Adult plants of Agrostis ten- 
uis growing on pasture soil displayed 
a high index of tolerance and so did 
their progeny. Clearly there was a 
great infiltration of tolerant genes into 
the pasture population. At 230 feet 
from the boundary, however, the en- 
tire situation was reversed. There par- 
ent plants had a tolerance index of 
three while that of their seedlings was 
much higher, between four and five. 
At the last station sampled, almost 
500 feet from the mine, progeny still 
displayed a relatively high tolerance, 
between three and four, although their 
parents, with an index of two, were 
nearly nontolerant. This phenomenon 
can only be explained by two proc- 
esses: the constant migration of tol- 
erant genes from the mine, which con- 
tinues to produce higher tolerance in 
seedlings each generation, combined 
with strong selection against metal- 
tolerant seedlings in nontolerant pas- 
ture populations. Tolerant genes, 
which adapt plants to growth in soils 
with high copper content, are acquired 
at a cost: such individuals cannot sur- 
vive in normal pasture populations. 
We do not fully understand the bi- 
ology behind this constraint. It may 
36 
