Fig. 1.

Differences in the temperature requirements for PTG of three species (Campanula alpina, Trollius europaeus and Gentiana asclepiadea) occurring in climatically contrasting habitats. The cardinal temperatures were estimated by fitting the generalized plant growth model to the experimental data for pollen tube length (see Materials and Methods section). The species relative abundances along the gradient of mean annual temperatures relate to the vegetation survey in the study area (see Materials and Methods section).