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Surface tension gradients in free crystal growth melts give rise to convective flow. If these gradients are due to thermal gradients, the well known thermocapillary (Marangoni) convection ensues. Concentration gradients due to segregation at the interface during growth can lead to additional solutocapillary convection. A system with large solutocapillary convection is Ge-Si due to the pronounced segregation and the strong difference in surface tension; solutal buoyancy convection is also present due to the large density difference between Ge and Si. Solutocapillary convection will oppose thermocapillary convection in the Ge-Si system since Si, having the higher surface tension, is preferentially incorporated into the crystal. A set of experiments directly proving and partially quantifying the effect has been conducted under microgravity during a parabolic flight campaign by recrystallizing Ge-Si mixtures of different compositions, between 3% and 9% Si, in a crucible with tracers to visualize the movement. Solutocapillary flow with initial flow rates in excess of 5.5 cm/s at the onset of crystallization was measured. A slight dependence of the flow velocity on the initial Si content has been found. Experiments on the ground showed the same effect but with overall smaller speeds; this difference can be explained by the additional action of solutal buoyancy convection. Dedicated to Prof. Wolfgang Neumann on the occasion of his 65th birthday

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Cavity spot of carrot, caused by several species of Pythium, is endemic in many carrot production areas of the world, including the Holland/Bradford Marsh region of Ontario, Canada. Field trials were conducted from 2002–04 to determine if carrots with different pigments varied in susceptibility to the disease. Carrots from the USDA breeding program at the University of Wisconsin were seeded in muck soil (pH 6.4, 60% organic matter) on 28, 30, and 27 May, harvested 22, 22, and 23 Oct., and assessed for disease on 5, 8, and 10 Dec. 2002, 2003, and 2004, respectively. The carrots were white (W 105-7), yellow (W 102-1), dark orange (W 101-23), red (W 104-3), and purple (W 106-3). Cultivar `Cellobunch' was included in 2003 and 2004. Twenty-five carrots of each of four replicate plots were assessed in 2002 and 2003, and 50 carrots were assessed in 2004, for disease incidence and severity [disease severity index (DSI), based on the size of the largest lesion per carrot]. Disease incidence was moderate in 2002 and 2003 (34%, 33%), and high in 2004 (60%). Consistent differences in susceptibility to cavity spot were identified over the three years of trials. The purple carrot had the lowest incidence (12%) and severity (7 DSI) of cavity spot, followed by the dark orange carrot (39%, 22 DSI) as compared to the susceptible yellow carrot (58%, 41 DSI). There was no difference in disease reaction between the yellow and white carrots. `Cellobunch' had the same reaction as the dark orange carrot. Studies are needed to determine whether the pigments themselves cause differences in the disease response.