The anatomy of a stalk of annual runaway Populus nervirubens Alb was studied. Specific features of anatomy of a core, xylem and phloem a poplar are established. It is revealed two types of cages in the centre of a core and variety of cages in a zone adjoining with xylem. Sieve elements phloem have a kernel. Presence of cytoplasm, kernels and a time of a cellular wall in phloem fibres and sklereid is noted. Fibres settle down groups with various number of separate fibres in groups. Between fibres presence intercellular space is revealed.