Some populations of white clover, Trifolium repens, are described as cyanogenic because they produce hydrogen cyanide. Hydrogen cyanide is a poison which inhibits respiration and reduces grazing by herbivores. A group of scientists investigated the percentage of cyanogenic plants in populations of T. repens growing in different locations. The mean January temperature was also recorded. Table 2.1 shows the results of their investigation. Table 2.1 location,percentage of cyanogenic T. repens,mean January temperature /°C Almora, India,85,12.2 Fairbanks, Alaska, USA,5,-23.9 Karaj River, Iran,64,4.4 Konosu, Japan,50,4.2 Lennoxville, Quebec, Canada,71,-10.0 Mandan, North Dakota, USA,33,-12.8 Novosibirsk, Russia,0,-19.4 Pretoria, South Africa,68,10.0 Rabat, Morocco,100,12.5 The scientists calculated the Spearman's rank correlation coefficient to test the hypothesis: The proportion of cyanogenic plants in populations of T. repens increases as the mean January temperature increases.