Influence of Flooding on Net CO2Assimilation, Growth and Stem Anatomy of Annona Species

A series of experiments was conducted to assess net CO₂assimilationand growth responses to waterlogging of grafted and seedlingtrees in the genus Annona. Seedlings of A. glabra, A. muricataandA. squamosa L., and scions of ‘Gefner’ atemoya(A. squamosaxA. cherimola Mill.), ‘49-11’ (‘Gefner’atemoyaxA. reticulata L.), ‘4-5’ (‘Priestley’atemoyaxA. reticulata), A. reticulata grafted onto either A.glabra, A. reticulata orA. squamosa rootstocks were floodedfor up to 60 d. Soil anaerobiosis occurred on the third dayof flooding. Seedlings ofA. glabra and A. muricata, and thescions ‘49-11’, ‘Gefner’ atemoya, andA. reticulata grafted onto A. glabra rootstock were consideredflood tolerant based on their ability to survive and grow inflooded conditions. Scions of the normally flood-sensitive A.reticulata, ‘Gefner’ atemoya, and ‘49-11’tolerated root waterlogging when grafted onto the flood-tolerantspecies, A. glabra. In contrast, flooding of A. squamosa seedlingsand rootstocks, and A. reticulata rootstocks greatly reducedgrowth and net CO₂assimilation rates, and resulted in 20–80%tree mortality. Stem anatomical responses to long-term flooding(12 continuous months) were assessed in seedlings of A. glabraand A. muricata, and trees of ‘49-11’ grafted ontoA. glabra. Flooded trees developed hypertrophied stem lenticels,particularly in A. glabra, and enlarged xylem cells resultingin thicker stems with reduced xylem density. Flooding did notincrease air spaces in pre-existing xylem near the pith or inxylem tissue that was formed during flooding. Thus, flood tolerancedid not involve aerenchyma formation in the stem. Copyright1999 Annals of Botany Company Flood tolerance, net CO₂assimilation, photosynthesis, stem anatomy, shoot growth, anaerobiosis, Annonaceae.     

Annual ryegrass toxicity: parasitism of Lolium rigidum by a seedgall forming nematode (Anguina sp.)*

Infection of annual ryegrass (Lolium rigidum) by Anguina sp. resulted in replacement of seeds by bottle-shaped galls, each containing several hundred quiescent, second-stage larvae. The biology of the nematodes, including the emergence of larvae from galls, survival in soil, and movement into and development within the host plant, has been examined. Larvae were not able to leave the galls during the dry summer, but emerged within soil 2–6 wk after normal autumn rains and following partial decay of the gall rind. Emergence took place over several months, and not all larvae emerged in any one year; they were able to survive over summer in soil both within and outside the galls. Under suitable moisture conditions, host plants were infested by larvae which climbed up the outer surfaces, became lodged within leaf sheaths, and then gradually moved towards the centre of the plant. Larvae which reached the central or axillary meristems prior to flowering were carried up with the elongating inflorescence, and attacked developing floret primordia. The nematodes developed rapidly to the adult stage, and eggs were being laid within galls by the time the inflorescence had emerged. Second-stage larvae hatched quickly and were the only live stage remaining after the ryegrass had died.     

Movement of lucifer yellow in leaves of Coleus blumei Benth

Abstract Individual spongy mesophyll cells in green areas of variegated Coleus blumei leaves were injected with the symplast-mobile dye lucifer yellow and its movement to other cell types was followed with fluorescence microscopy. In 13 trials, the dye remained in the injected cell twice, moved only to other mesophyll cells five times, and moved up to and along minor veins six times. Where extensive movement of the dye occurred, the tissue was fixed with 4% glutaraldehyde, dehydrated, embedded in plastic, sectioned at 3 μm, and examined again with fluorescence microscopy. The dye was found in abaxial bundle-sheath cells for up to 200 μm or more distant from the site of injection near the minor vein, but no convincing evidence was found for its presence in the vascular tissue itself. It thus appears that superficial whole-mount views of lucifer yellow movement along leaf minor veins cannot be taken as certain evidence for symplastic transport of the dye into and along the vascular tissues.     

Statistical Confusion Among Graduate Students: Sickness or Symptom?

Abstract: Statistics is one of the most important yet difficult subjects for many ecology and wildlife graduate students to learn. Insufficient knowledge about how to conduct quality science and the ongoing debate about the relative value of competing statistical ideologies contribute to uncertainties among graduate students regarding which statistical tests are most appropriate. Herein, we argue that increased education of the available statistical tests alone is unlikely to ameliorate the problem. Instead, we suggest that statistical uncertainties among graduate students are a secondary symptom of a larger problem. We believe the root cause lies in the lack of education on how to conduct science as an integrated process from hypothesis creation through statistical analysis. We argue that if students are taught to think about how each step of the process will affect all other steps, many statistical uncertainties will be avoided.