Estimation of Provisional Seed Viability Constants for Apple (Malus domestica Borkh. cv. Greensleeves)

Estimates of viability constants have been calculated for apple(cv. Greensleeves) seeds, stored hermetically in a range ofenvironments. The constants allow reasonable prediction of seedstorage life (orthodox), at least in the short and medium term. Apple, Malus domestica Borkh. cv. Greensleeves, seed storage, viability constants, influence of seed moisture content and temperature     

Prefeeding larval development time is not correlated with egg size in regular echinoids (Strongylocentrotus species)

Summary

We compared prefeeding development times, from fertilized egg to prism larva, for Strongylocentrotus embryos from four clutches of eggs (each from a different species) differing in size. Development times did not vary consistently with egg diameter, and trends among eggs of different sizes varied with stage of development. In some cases, development times for eggs of intermediate diameter (S. franciscanus) were longer than those for larger or smaller eggs. Although mean egg diameters in clutches ranged from 84 μm (S. purpuratus) to 162 μm (S. pallidus), differences in development time to the last embryonic stage (prism) were very small. We conclude that the inverse relationship between parental investment in offspring and premetamorphic development time in echinoids depends only on the functional consequences of reduced size of feeding larval stages: effects of egg size on prefeeding development time are not evident.     

Analysis of the Effect of Cold Stratification on the Germination Response to Light and Alternating Temperatures using Selected Seed Populations of Ranunculus sceleratus L.

From a single population of achenes (seeds) of Ranunculus sceleratusL. sub-populations were selected on the basis of the sensitivityof individuals to an increasing number of daily light/temperatureshift cycles. Each cycle comprised a 4 h pulse of red lightfollowed by a 4 h temperature shift from 16 to 31 ?C. Selectionfor low dormancy (NND and ND) and high dormancy (D and DD) populationsresulted in a > 5-fold difference in the number of cyclesrequired for 50% germination. Despite a shift in the mean levelof dormancy the distributions of sensitivity (slopes of dose-responsecurves) were similar in all four selected populations. Differentialeffects of cold stratification on the germination response tolight and alternating temperatures were related to the depthof primary dormancy. The proportion of individuals that respondedpositively to the dormancy breaking effects of cold stratificationfollowed the trend DD < D < ND < NND. In high dormancypopulations (D and DD) the rate and uniformity of germinationof some individuals was reduced by cold stratification, indicatinga dormancy inducing effect. Over the range 2 to 11 ?C the effectivenessof dormancy release or dormancy induction was inversely relatedto temperature. The effects of cold stratification on the expressionof dormancy in R. sceleratus are discussed in relation to areproductive strategy involving winter and summer annual behaviour. Key words: Cold stratification, selection, dormancy, light, alternating temperatures, germination     

Component growth efficiencies of mycorrhizal and nonmycorrhizal plants

Two mycotrophic species ( Lactuca sativa and Abutilon theophrasti ) and one nonmycotrophic species ( Beta vulgaris ) were grown in a P-deficient soil, and the effects of mycorrhizal inoculation on three variables that determine growth rate were assessed for each. The phosphorus-use efficiency (PUE, d W /d P ) is the ratio of d. wt increase to P content increase. Plant P is the amount of P (the limiting resource) controlled by the plant, which can be allocated to various purposes. The phosphorus efficiency index (PEI, d P / P d t ) is the efficiency with which plant P is used to acquire P from the soil. Inoculated and control plants of a given species initially contained the same amount of P because all plants were grown from seed. Mycorrhizal colonization significantly increased the PEI of Lactuca and Abutilon (by 23 and 32%, respectively). As expected, mycorrhizal inoculation did not significantly increase the PEI of Beta . As a result, mycorrhizal inoculation significantly increased the P content of Lactuca and Abutilon , but not Beta . Mycorrhizal colonization decreased the PUE of lettuce, but did not significantly affect that of Abutilon or Beta . Mycorrhizal inoculation therefore slightly increased the growth rate of Lactuca , greatly increased the growth rate of Abutilon , and ultimately had no significant effect on the growth rate of Beta .     

Comparative leaf anatomy of the Penaeaceae and its ecological Implications

The leaf anatomy of species representing all seven genera of the Penaeaceae was studied by light and scanning electron microscopy. Due to variability and inconsistency, leaf anatomical characters are not regarded as particularly useful for systematics within or among genera in this family. Across the family, a number of taxa exhibit a trend towards amphistomatous, isobilateral leaves, generally associated with increased leaf thickness and amount of palisade mesophyll. This trend is not apparent in closely related families, e.g. Alzateaceae, Cryp-teroniaceae, Oliniaceae and Rhynchocalycaceae. Most species are found in comparatively mesic habitats and it is difficult to postulate primary xeromorphic trends in leaf anatomy. The sclerophylly encountered across the family as a whole is likely to be related to paucity of soil nutrients rather than a response to water stress.