Breaking tuber dormancy in Helianthus tuberosus L. and interspecific hybrids of Helianthus Annuus L. × Helianthus tuberosus
Tubers of Helianthus tuberosus L. are dormant after production in the late fall until the next spring. In the wild, tuber dormancy is broken after exposure to winter cold, resulting in sprouting and shoot development in the spring when conditions are favorable. The dormancy period typically limits H. tuberosus populations to one growth cycle per year. An efficient method for breaking tuber dormancy is needed to have an additional growth cycle per year in a breeding program, which could take place in winter inthenurseryorthegreenhouse allowingforincreased breedingefficiency.Theobjective of thisresearch was to compare chemicaland cold temperature treatments for artificially breaking tuber dormancy in 12 genotypes of H. tuberosus and interspecific hybrids of Helianthus annuus L. 3 H. tuberosus. Five cold exposures (2, 4, 6, 8, 10 weeks at 2 8C), three plant hormones (ethylene, cytokinin, and gibberellic acid), and one untreated control were examined. Gibberellic acid was the best chemical treatment, initiating plant growthwithin6.5to11.5daysinthemajorityofgenotypestested.Thebestcoldtreatment was exposure to 2 8C for 8 weeks, where plant growth began 63.6 to 67.5 days after treatment initiation. Although longer cold treatments shortened the time to emergence while in the greenhouse, the penalty of the long cold treatment per se was too long to be useful. The gibberellic acid treatment strategy described here may not need further optimization, because it is short enough to allow for two growth cycles of H. tuberosus per year.
The Fate of 1,2‐14C‐(Chloroethyl) Phosphonic Acid (Ethephon) in Olive (Olea europea)
The translocation and metabolism of ethephon at pH 7.0 and its effect on abscission of olive fruit, were studied in attached and detached fruits. In detached olives, the lowest fruit removal force values were achieved when the fruits were treated at their proximal cavity and kept under humid conditions. Following application of 14C-ethephon to the proximal cavity 63% of the label was absorbed within 4 h; evolution of 14C-ethylene proceeded at a slow rate, mainly from 14C-ethephon remaining on the olive surface, totaling 37% of the applied ethephon in 20 days. 14C-ethephon disappeared rapidly after its application to olive on the tree. More 14C-ethephon could be extracted from olives on the trees after distal application than after proximal application. 
 
 
 
Since the response of detached olives to treatments with ethephon was similar to that of attached olives in regard to fruit removal force reduction, the former can be used for the study of many aspects of ethephon and ethylene metabolism in olives. 
 
 
 
In our study no ethephon metabolites other than 14C-ethylene could be detected after 14C-ethephon application to attached or detached olive fruits.
Formation and Strength of Magnesia Whiskers
The formation of single-crystal magnesia whiskers during the compressive deformation of single crystals at room temperatures is described. These whiskers can have strengths of the order of millions of pounds per square inch. They are formed during fracture as a result of the discontinuous propagation of cracks which are mechanically relieving internal stresses resulting from plastic flow