The Geography of Phytochemical Races

2.7 North and Central America 103
between desert and nondesert plants, however. With only one exception (fl ower buds
from Anza-Borrego plants), tissues from desert plants had higher concentrations of
the glucosinolate than those from more moderate environments. Experiments with
Isomeris grown under laboratory conditions revealed that glucocapparin content
varied inversely with soil nitrogen, suggesting that the availability of this element
in nature strongly infl uences the formation of the defense compound, which is in
accord with the views of Coley et al. (1985) who hold that species that grow slowly
owing to limitations of resources evolve “immobile defenses” (phenolic compounds
or fi ber) whereas “mobile defenses” are produced by plants that are capable of rapid
growth in the presence of ample resources. Isomeris arborea, which is capable of
rapid growth (Blua et al., 1988), falls within this latter category.
2.7.13 Soils and Asters
One of the earliest studies of variation involving fl avonoids was that of Abrahamson
and Solbrig (1970) who examined these compounds, including an analysis of total
anthocyanins, in several species of Aster along a transect running from extreme
northwestern Pennsylvania to eastern Massachusetts. Soil and plant samples were
taken from 19 sites. Soil samples were examined for a variety of features: nitrate
content, moisture, color, and clay content. Plants were taken to the University of
Michigan Botanical Gardens where they were maintained in a uniform garden environment.
Extracts of the cultivated plants were analyzed by paper chromatography
and total anthocyanin (determined to be cyanin) content was determined colorimetrically.
The species were identifi ed as A. ciliolatus Lindl. (two sites), A. cordifolius L.
(12 sites), A. lowreianus Porter (one site), and A. undulatus L. (one site). Considerable
variation was seen in the chromatographic profi les, with six compounds
(spots, actually) common to all 83 plants, ten present in over 60 plants, and nine
variable within populations. No compound (spot) was species specifi c. Anthocyanin
concentration also varied without evident pattern. Likewise, there appeared
to be no relationship between fl avonoid profi les and soil. Signifi cantly different
chromatographic profi les were observed at different times throughout the growing
season, which led the authors to caution future workers to be wary of randomly collected
samples and to make use of common garden studies whenever possible. Their
advice has not always been followed.
2.7.14 Lupinus sericeus (Fabaceae)
In this example, individual plants of Lupinus sericeus Pursh were collected over a
distance measuring approximately 1500 km, including most of the range of the species.
In practice, this amounted to a north–south transect running from the Alberta-
British Columbia border to northern Arizona. Lupinus sericeus occurs from southeastern
British Columbia and southwestern Alberta to the Kaibab Plateau in northern Arizona,