Bud abortion in tulip bulbs studied by magnetic resonance imaging

After storage and subsequent planting of flower bulbs, the flower bud frequently appears to be aborted. This physiological aberration is probably caused by a change in the water status of the bulb and may be initiated during storage. The development of bud abortion in tulip bulbs was studied during long-term dry storage of the bulbs at 5 °C. The anatomy of individual tulip bulbs was followed non-invasively with T2-weighted NMR imaging, which allowed the monitoring of the growth of the shoot and daughter bulbs. Quantitative maps of T1 and T2 relaxation times of individual bulbs were used to assess regional changes in the water status of different tissues. Parallel to the NMR measurements, bulbs were planted to assess the ultimate flower quality. Moreover, water content, osmolality of tissue sap and ion leakage of excised shoot and scale tissues were determined to obtain information about the water status and viability of the bulbs. Significant decreases during long-term storage were found in T1 and T2 relaxation times in the shoot and particularly in the stamens. An increase in the osmolality of tissue sap and the decrease in relaxation times in the shoot below a certain threshold value attained after 24 weeks of storage, could be indicative for the emergence of bud abortion in tulip

Learner Performance in Multimedia Learning Arrangements: An Analysis Across Instructional Approaches

Eysink THS, Jong T de, Berthold K, Kolloffel B, Opfermann M, Wouters P. Learner Performance in Multimedia Learning Arrangements: An Analysis Across Instructional Approaches. American Educational Research Journal. 2009;46(4):1107-1149.In this study, the authors compared four multimedia learning arrangements differing in instructional approach on effectiveness and efficiency for learning: (a) hypermedia learning, (b) observational learning, (c) self-explanation— based learning, and (d) inquiry learning. The approaches all advocate learners' active attitude toward the learning material but show differences in the specific learning processes they intend to foster. Learning results were measured on different types of knowledge: conceptual, intuitive, procedural, and situational. The outcomes show that the two approaches asking learners to generate (parts of) the subject matter (either by self-explanations or by conducting experiments) led to better performance on all types of knowledge. However, results also show that emphasis on generating subject matter by the learner resulted in less efficient learning