Time to flower in Pelargonium Xhortorum Bailey, whether expressed as time to visible flower bud or first anthesis, is most dependent on the first 6-8 true leaves (“critical” leaves). Flowering time was correlated with leaf area of the critical leaves but not with total leaf area. Removal of young leaves did not accelerate flowering but resulted in more flowers on the first inflorescence. If the 6-8 critical leaves occurred within the first 8-10 nodes, then flowering was not inhibited. A minimum of 15 nodes was necessary for flowering, but node number ranged from 15-23. Time from visible bud to anthesis was not affected by defoliation, leaf area, or position of critical leaves.
Floral initiation and development in the hybrid geranium, Pelargonium X hortorum Bailey, were examined using scanning electron microscopy. Inflorescence initiation was marked by a raising of the apex followed by the formation of convex flower primordia. In floral development, 5 sepal primordia were delimited, closely followed by 5 petal primordia. Imbricate sepals enclosed the floral apex during later developmental stages. Five antesepalous, then 5 antepetalous stamen primordia were initiated. Five gynoecial primordia arose, forming a pentagonal ridge, carpellary lobes, and eventually an elongate style with stigma. Three of the antepetalous stamen primordia developed into filaform starninodia.
Light and temperature responses of whole-plant CO2 exchange were determined for two cultivars of Angelonia angustifolia Benth., `AngelMist Purple Stripe' and `AngelMist Deep Plum'. Whole crop net photosynthesis (Pnet) of `AngelMist Purple Stripe' and `AngelMist Deep Plum' were measured at eight temperatures, ranging from 17 to 42 °C. Pnet for both cultivars increased from 17 to ≈20 °C, and then decreased as temperature increased further. Optimal temperatures for Pnet of `AngelMist Purple Stripe' and `AngelMist Deep Plum' were 20.8 and 19.8 °C, respectively. There was no significant difference between the two cultivars, irrespective of temperature. The Q10 (the relative increase with a 10 °C increase in temperature) for Pnet of both cultivars decreased over the entire temperature range. Dark respiration (Rdark) of both cultivars showed a similar linear increase as temperature increased. As photosynthetic photon flux (PPF) increased from 0 to 600 μmol·m-2·s-1, Pnet of both cultivars increased. Light saturation was not yet reached at 600 μmol·m-2·s-1. The light compensation point occurred at 69 μmol·m-2·s-1 for `AngelMist Purple Stripe' and at 89 μmol·m-2·s-1 for `AngelMist Deep Plum'. The lower light saturation point of `AngelMist Purple Stripe' was the result of a higher quantum yield (0.037 mol·mol-1 for `AngelMist Purple Stripe' and 0.026 mol·mol-1 for `AngelMist Deep Plum'). The difference in quantum yield between the two cultivars may explain the faster growth habit of `AngelMist Purple Stripe'.