Anatomy and mechanics of the stem and lateral roots of cleavers (Galium aparine L.)

Cleavers (Galium aparine L.) is a fast growing herbaceous annual with a scrambling-ascending growth habit. Biomechanical data are further discussed with reference to the plant’s growth habit and mechanical environment. Mature plants often use upright species for support and are common in hedgerows and on waste ground. The morphology and mechanics of mature cleavers was investigated using plants grown in pots and ones collected from the grounds at the University of Lincoln, Lincoln, UK. Tensile tests were carried out on the stem and the basal section of the first-order lateral roots. The net orientation of cellulose microfibrils in the cell walls was investigated using polarised light microscopy. Results show that the basal region of the stem and first-order lateral roots was highly extensible. Breaking strains of 24±7% were recorded for the stem base and 28±6 % for the roots. Anatomical observations showed that the basal region of the stem was dominated by a central core of vascular tissue with little or no pith. The net orientation of wall microfibrils in the secondary xylem diverge from the longitudinal by approximately 9˚. The mechanism by which the stem is able to withstand such high breaking strains is unclear; reorientation of the cellulose fibrils in the stem along the axis of loading is not thought to be exclusively responsible