When plants of Sedum rosea (L.) Scop, and

S. telephium L. ssp. fabaria Syme are grown in competition at different altitudes it is found that the growth of the species is affected differentially. This effect is such that at low altitudes S. telephium is a larger plant than S. rosea, while the reverse is the case at high altitudes. The observed differences are caused by a marked sensitivity of the growth of S. telephium to differences in altitude, while S. rosea is very insensitive.

The most probable cause of these responses would appear to be differences of climate. The influence of altitude in northern England on air temperature, saturation deficit and irradiance has been investigated in order to establish the magnitude of the differences which may cause these responses.