GROWTH ORIENTATION OF UNDERGROUND SHOOTS IN PERENNIAL HERBACEOUS PLANTS .3. MORPHOPHYSIOLOGY OF UNDERGROUND SHOOTS AND SARMENT DEVELOPMENT

The growth orientation and development of underground shoots producing sarments were studied in a series of tuberous plants including Solanu m demissum Lindl., S. acaule Bitt., S. molinae Juz., Helianthus macrop hyllus Willd., and Ullucus tuberosus Caldas. Morphophysiological prope rties of sarments as compared to rhizomes and stolons, were identified . In the course of differentiation, the sarment apical zone produced l eaf primordia during underground diatropic growth. Before light-depend ent differentiation the sarment apex exhibited a negative phototropic response mediated by the phytochrome system. Such phytochrome-mediated control of diatropic growth orientation operated till the appearance of leaf primordia. Leaf primordia formation completed the period of un derground diatropic growth, then the shoot protruded through the soil, occupied an above-ground orthotropic position and developed into the plant.