In order to investigate the physiological differentiation occurring within a species, samples of sixty tillers of a number of populations of Agrostis tennis were transplanted into experimental plots established in various contrasting natural habitats in the neighbourhood of Aberystwyth in central Wales. Two populations were also grown on lead-contaminated soil. Their performance under the different environments was examined. It was found that:
- (i) Populations originating from contrasting habitats differed considerably in their ability to tolerate different extreme conditions. For instance, the growth of lowland populations in the upland plot was seriously affected by winter conditions, and the growth of upland populations in the coastal plot was affected by salt storm spray. The population from a lead mine was able to grow in lead-contaminated soil, while the population from normal pasture was not. The behaviour of each population could always be related to the environment from which the population originated.
- (ii) These differences were also found, although on a smaller scale, between populations originating from less contrasting environments.
- (iii) Populations originating from habitats only a short distance apart showed considerable differences in performance in those cases where the original habitats were markedly different.
- (iv) Such physiological differentiation was not necessarily accompanied by morphological differentiation. It is likely that this is because the two types of differentiation are in relation to unrelated factors of the environment.
It was concluded that the pattern of physiological differentiation was a graded patchwork similar to the pattern of morphological differentiation previously described.