The Butcher Block Kitchen Work 
Center is a convenient counter extender 
or an efficient work island... and the 
focal point of the kitchen you'll be proud 
of. Outstanding quality at a very reason- 
able price. 
• Solid Rock Maple -- 
handcrafted in Vermont. 
• Non-stick Butcher Block top 
2'x3’, standard counter height 
• Locking casters roll easily 
and stay put. 
• 2’x3’ lower storage shelf. 
• Child-safe knife rack - many 
other features, too! 
Send today for 
FREE details! 
Garden Way 
Research 
Charlotte, VT 05445 
Butcher Block 7 V G arde " Way Research 
... ... , _ . Dept. A1041K 
Kitchen Work Center charlotte. VT 05445 
Beauty and 
Versatility Combined. 
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Let Them Grow With a Questar 
Children with intense curiosity about the nature of 
things will learn to master many tools, and the tele- 
scope, that prime tool of science, should be the first. 
Only the finest telescope, combining mechanical 
and optical perfection, can become a true ex- 
tension of the mind and hand. Such an instrument 
is the Questar, and its lovely versatility adds an 
extra dimension to many fields: astronomy, terres- 
trial studies, or perhaps simply to the pure 
enjoyment of vyildlife. What else could you buy a 
child that would enchant, amuse and continue to 
serve for a lifetime? 
Send for our booklet in color on the portable, 
photovisual Questar $2, please, to cover mailing 
on this continent Airmail to S A , $3.50; Europe 
and N Africa, $4 elsewhere, $4. 50. 
QUESTAR 
Box GY, New Hope, Pa 18938 (215) 862-5277 
vigorously with the wide array of other 
species in the field. The two popu- 
lations meet at the boundary of the 
toxic soil. Since these plants are pol- 
linated by wind, some pollen from 
each side fertilizes plants on the other 
side. As a result, some offspring on 
the mine side of the boundary should 
inherit nontolerant genes, and seed 
produced on the pasture side should 
display some tolerance. 
This movement of genes in both 
directions could be expected to create 
an array of tolerances among offspring 
and a continuous transition zone from 
very tolerant plants well into the mine 
to very intolerant plants well into the 
pasture. Surprisingly, there is a very 
sharp break in the tolerance of the 
two populations, and the border be- 
tween them is a clearly defined, sharp 
line. Although mine and pasture plants 
are only inches apart at the boundary, 
the mine individuals are fully tolerant, 
whereas the neighboring pasture 
plants fail to grow in the smallest con- 
centrations of heavy metals. How is 
such a distinct boundary maintained 
in spite of the flow of genes back 
and forth between mine and pasture? 
A critical tension exists between this 
movement of homogenizing genes be- 
tween two different Agrostis popula- 
tions and the selective factors working 
to maintain particular qualities of the 
populations. When wind-borne pollen 
carrying nontolerant genes crosses the 
border and fertilizes the gametes of 
tolerant females, the resultant off- 
spring show a range of tolerances. The 
movement of genes from the pasture 
to the mine would, therefore, tend to 
dilute the tolerance level of seedlings. 
Only fully tolerant individuals survive 
to reproduce, however. This selective 
mortality, which eliminates variants, 
counteracts the dilution and molds a 
totally tolerant population. The pas- 
ture and mine populations evolve dis- 
tinctive adaptations because selective 
factors are dominant over the homog- 
enizing influence of foreign genes. 
Thus evolution — the continuous 
sculpting of particular physiologies, 
morphologies, and behaviors — is ac- 
complished through the differential 
survival of variants created in repro- 
duction. Plants, because they do not 
move, lend themselves to observation 
of the process of evolution. The par- 
ticular elegance of studying metal tol- 
erance in Agrostis lies in our ability 
to measure variation and watch how 
it changes with each generation. Nat- 
ural selection, which may ordinarily 
run long and slow, is captured in the 
act, held for inspection by the op- 
posing flow of genes. 
Tom McNeilly, a student of Brad- 
shaw’s, separated the effects of se- 
lection from the flow of genes by ob- 
serving a population of Agrostis tenuis 
he found growing on a derelict copper 
mine in Caernarvonshire, Wales. The 
mine’s surface, less than 985 feet 
across, sits on the floor of a U-shaped, 
glaciated valley whose steep slopes are 
covered with sheep pasture. McNeilly 
suspected that the east-west orienta- 
tion of the valley, which strongly po- 
larizes the prevailing winds in a west- 
erly direction, might provide an 
appropriate setting for his work. 
Toward the end of the summer, 
McNeilly collected seeds from a group 
of marked adult plants on the mine. 
He germinated thirty seeds and sub- 
jected the seedlings to the tolerance 
test in a nutrient solution with a toxic 
concentration of copper. The marked 
adults were then transplanted to a 
greenhouse where, isolated from the 
pasture plants, they formed a new 
batch of seeds exclusively through the 
exchange of pollen among themselves. 
These greenhouse seeds were also ger- 
minated and their seedlings tested for 
tolerance. Finally, the marked adults 
themselves were subjected to the cop- 
per solution. McNeilly could then 
compare the tolerance of adult plants 
with that of their greenhouse off- 
spring; the tolerance of the same adult 
plants with that of their mine off- 
spring; and, finally, the tolerance of 
the mine offspring with that of the 
greenhouse offspring. 
The adult plants displayed a rel- 
atively narrow range of tolerance and 
had an average index between six and 
seven. A few individuals were as low 
as five, but considerably more dis- 
played a high tolerance of seven. The 
seedlings that germinated from the 
isolated greenhouse seed also dis- 
played an average tolerance between 
six and seven. As expected in off- 
spring, however, the range of tolerance 
was greater: one of the seedlings was 
as low as three, while another, at ten, 
was completely tolerant. This wider 
variability among offspring compared 
with parents is the result of the re- 
combination of genes, through sexual 
reproduction, into many different sets 
among the progeny. Because the aver- 
age indexes of adults and their off- 
spring were identical, we can conclude 
that the expression of tolerance is con- 
trolled by genes. Of more interest is 
32 
