Xylem, Phloem and Transpiration Flows in Developing Apple Fruits

Xylem, phloem and transpiration flows were measured in developingfruits of the apples Royal Gala and Cox's Orange Pippin at early,mid and late stages during their development. Fruit volume growthwas first computed from measurements of diameter made usinga system of sensitive displacement transducers. Xylem, phloemand transpiration flow components (of which fruit volume growthis the integral) were then separated using a scheme of treatmentswhich disabled one or other flow at a time. Changes observed during development in the patterns of the threeflows are in general agreement with expectations based on lessdirect observations (loc. cit. Ferguson and Watkins, 1989).Recognizing the distinctive mineral compositions of xylem andphloem streams, the changes also accommodate, and seem to explain,published observations of mineral accumulation in apple. Significant differences in the pattern of xylem and phloem flowwere observed between the varieties examined. These may explainvarietal differences in susceptibility to the mineral imbalancedisorder bitter-pit. Xylem flows were shown to reverse at times; that is they flowedfrom fruit to tree. This occurred particularly during periodsof high evaporative demand. Xylem reversal is of importanceto the overall water economy of a tree but may also have specialimportance to the mineral composition of the fruit. Key words: Mineral nutrition, bitter-pit, apple, xylem, phloem, transpiration, water balance     

Late Palaeozoic mollusc reproduction: cephalopod egg-laying behavior and gastropod larval palaeobiology

Faunal analysis of an oxygen‐depleted marine Lower Carboniferous succession (Late Mississippian Ruddle Shale) suggests how some cephalopod taxa laid their eggs during the Late Palaeozoic. At the Ruddle Shale collecting site in Arkansas, USA, the facies and overall fauna suggest severe oxygen depletion at the sediment/water interface. The Ammonoidea, with their small egg size, were probably laid in suspended gelatinous egg‐filled masses in the water column above the bottom or by attachment of the egg masses to floating debris. The ammonitella embryos developed within the suspended or attached egg mass; hatched individuals became part of the free‐swimming plankton biota. Based on shell morphology the Bactritoidea probably followed the same reproductive pattern. Coiled nautiloids (the Nautilida) and most orthoconic nautiloids (mostly the Pseudorthocerida) probably did not lay their eggs in the mid water column or as floatant attachments. This conclusion is based on the fact that, with one exception, all shells recovered of these two nautiloid orders are well past hatching. Gastropods in the Ruddle Shale are very small and cannot be visually detected in the field. However, microgastropods are abundant in washed residues. Most specimens are much smaller than 1 mm. The largest caenogastropod specimen is 1.3 mm high. These caenogastropods represent isolated larval shells and a successful metamorphosis was impossible because of oxygen depletion on the bottom. Allegations that a size of more than 1 mm is too large for pelagic larvae are refuted by examples of planktotrophic larval shells of modern gastropods (more than 1 mm high) and Triassic caenogastropods (up to 2 mm high) from the Cassian Formation (Northern Italy, South Alps). Repository information is given for the type‐material of the gastropod species Nuetzelina striata  Bandel, 2002 and Anozyga arkansasensis  Bandel, 2002 which were both erected based on specimens from the Ruddle Shale that were illustrated by Nützel & Mapes in 2001.