The present invention relates to altering the biomass and/or structure of a plant, in order to maximise its potential as a source of feedstock or increase its potential as a feedstock for the paper industry. CLE41 and/or CLE42 are used to manipulate growth and structure of the vascular tissue of the plant. The present invention also provides plants in which the levels of CLE41 and/or CLE42 are increased compared to those of a native plant grown under identical conditions, and parts of such plants. Also provided are methods for using such plants or plant parts in the production of plant derived products such as paper or biofuels.