EXPERIMENTAL CONTROL OF THE SHOOT SYSTEM IN SPORELINGS OF PTERIDIUM AQUILINUM

The shoot system of Pteridium develops from a simple, upright sporeling type through a rhizomatous leaf-bearing form, into a complex system with rapidly growing, leafless long shoots and slowly growing, leafy lateral branches or short shoots. Transitional stages axe available in sporeling material and ontogeny may be controlled by specific carbohydrate levels. At concentrations of sucrose below 2% a rhizomatous sporeling plant may be maintained indefinitely in the leaf-bearing state. At 2–8% sucrose, the short shoot habit becomes established, and at 4–8% it may be reliably stabilized. If concentrations up to 5 mg/liter of kinetin are added to cultures of intact plants or to excised short and long shoot apices of plants, the long shoots expand slowly into determined (no further growth possible even on transfer back to basal medium) club-shaped tips. The short shoot apices, by contrast, quickly proliferate into callus-like masses and will re-form organized meristems over the entire lobulate surface on transfer to medium lacking kinetin. The morphogenetic significance of these findings is discussed.