Different concentration ratios of carbon and nitrogen compounds in nectar, phloem sap and whole leaves from <i>M. barclayana, L. erubescens</i> and <i>B. napus.</i>

Abbreviations: n.c. = non-calculable because one sugar concentration was zero 1Sum of C and sum of N were calculated by multiplication of the number of C or N atoms in the analyzed carbohydrates and amino acids with the sum of concentrations of carbohydrates and amino acids.