Frequency of fold change values in the down-regulated gene-set after Gelsemium s. treatments. In this analysis the 49 genes whose expression was down-regulated by Gelsemium s. 2c were considered. Mean Log2 fluorescence values from Gelsemium s.-treated samples (Gnc) and those from controls (Ctnc) were obtained from 4 microarray experiments and their difference was considered as fold change attributable to Gelsemium s. effect (see Methods). Absolute fold changes less than or equal to 0.05 were considered null. Blue bars: frequencies of genes with negative fold change (< -0.05); grey bars: frequency of unaffected genes (from -0.05 to 0.05); pink bars: frequencies of genes with positive fold change (> 0.05). Fisher exact p values are reported in each panel except the G2c-Ct2c that are significant by definition.