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1. In view of the contrasting ecologies of the closely related species Veronica chamaedrys, V. montana and V. officinalis, the morphological effects of changes in light quality and quantity were investigated using the technique of growth analysis. By definition, the term |weight ratio' refers to the quotient of the dry weight of a particular organ to the total dry weight of the plant. 2. Three light climates were investigated: unshaded; muslin shaded (c. 37% full daylight, with no change in light quality); canopy shaded, using Ricinus zanzibariensis, also about 37% full daylight, but with lowered red:far-red (R:FR) ratio. 3. There were no species differences in relative growth rate (the efficiency of growth) or unit leaf rate (the assimilatory efficiency of the leaves). Although both rates fell with photon flux density (PFD), only relative growth rate decreased when R:FR ratio was also lowered. 4. Leaf area ratio (total leaf area as a quotient of total dry weight per plant) and specific leaf area (the relative thinness of the leaves) increased with reduced PFD, although the magnitude was species specific, with V. officinalis being least susceptible to change. Low R:FR ratio partially inhibited the increase of leaf area ratio in V. montana and both specific leaf area and leaf area ratio in V. chamaedrys, whereas it had no influence on V. officinalis. 5. Whilst leaf weight ratio was stable in V. officinalis, it was significantly smaller under low PFD in both V. chamaedrys and V. montana. Leaf weight ratio was further reduced by low R:FR ratio in V. montana. 6. Stem weight ratio and petiole weight ratio were increased by both low PFD and low R:FR ratio. Stem weight ratio was ranked in the order V. chamaedrys > V. montana > V. officinalis. V. montana allocated most biomass to petiole. In full light V. chamaedrys and V. officinalis had similar petiole weight ratios but V. officinalis exhibited a greater increase when shaded. 7. Root weight ratio fell with PFD. Sensitivity to R:FR ratio was manifest only in V. officinalis, which consistently had the greatest root weight ratio of the three species whereas V. montana had the lowest. 8. The ability to increase stem weight ratio in response to shading, whilst simultaneously reducing leaf weight ratio and root weight ratio, is suggested as maximizing the carbohydrate economy of the plant. On this premise, V. officinalis is least well adapted to long-term shading, whilst V. chamaedrys and V. montana are equally well suited. 9. Growth form in all three species dictates that increasing stem and petiole biomass results in greater horizontal spread and may confer the ability to forage for light. With respect to both the proportion of biomass allocated to stem, and its sensitivity to PFD and R:FR ratio, V. officinalis exhibits least propensity to forage. The petioles of both V. officinalis and V. montana may be of particular importance for the acquisition of light in shaded habitats.

1. Veronica chamaedrys, V. montana and V. officinalis were grown in either shaded or unshaded conditions in a field experiment lasting 18 months. V. officinalis failed to grow beneath shading as a result of slug grazing. Between May and October of the first year, unshaded V. officinalis had the highest relative growth rate (RGR) and shading significantly reduced RGR in both V. chamaedrys and V. montana but to a greater extent in V. chamaedrys. 2. The proportion of biomass allocated to roots was rapidly reduced by shading, but at the end of the experiment differences between species and light environments were negligible. Root phenology was unaffected by shading. In unshaded plants, allocation to stem (SWR) was higher in both V. chamaedrys and V. montana than in V. officinalis. Shading increased SWR and allocation to petioles but only altered stem phenology. The difference in SWR between shaded and unshaded plants of V. montana became less with time. Total allocation to leaves (TLWR) in unshaded plants was ranked V. montana > V. officinalis > V. chamaedrys. The contribution of dead leaves to TWLR was greatest in unshaded plants. Shading increased TLWR in V. chamaedrys but not in V. montana. 3. In unshaded plants, biomass allocation to sexual reproduction was ranked V. officinalis > V. chamaedrys > V. moiziana. Whilst shading reduced allocation to sexual reproduction in V. chamaedrys, it increased allocation in V. montana. Inflorescences were subdivided into: pedicels plus peduncles; capsules plus calyces; and seeds. A second quotient (|relative allocation') was devised by expressing the biomass allocated to each of these subgroups as a proportion of the total allocated to inflorescences. Whereas shading had no influence on relative allocation in V. montana, there was an increase in the pedicel + peduncle component in V. chamaedrys. Pedicels + peduncles accounted for 50% of inflorescence biomass in unshaded V. chamaedrys, but only 30% in V. montana and V. officinalis. Relative allocation to seeds was ranked V. montana > V. officinalis > V. chamaedrys. 4. Growth form, photosynthetic characteristics and slug grazing all hindered the proliferation of V. officinalis under shading. V. officinalis had a high RGR and allocated c. 25% of plant biomass to inflorescences. 5. Shading modified allocation within and between vegetative and reproductive organs of V. chamaedrys. V. chamaedry did not acclimatize to shading; increases in SWR in the second year, coinciding with tree canopy expansion, were supplementary to those incurred in the first year. 6. Shading had little effect on the allocation of biomass within either vegetative or reproductive organs of V. montana: changes detected in previous short-term experiments were transient. At high irradiances, V. montana was susceptible to chlorophyll photodegradation and could not sustain sexual reproductive output.

1. Veronica chamaedrys, V. montana and V. officinalis were grown outside, in a loam/grit soil, for 18 months either in full light or subject to canopy shading. V. officinalis failed to grow in shade. Vegetative and reproductive organs were analysed for nitrogen, phosphorus, potassium, calcium, magnesium and ash. The proportion of the total amount of a particular element in a plant that is allocated to a specific organ can be expressed as a quotient of the proportion of total plant biomass (i.e. carbon) allocated to that organ. The allocation index (AI) was calculated for each element and each organ. 2. Shading increased nitrogen and potassium concentrations in all organs, which is suggested to be symptomatic of an imbalance between nitrogen metabolism and carbon fixation. Leaf nitrogen Als, however, were lower in shaded plants, indicating that a constrained photosynthetic activity reduces the sink strength of leaves for nitrogen. 3. Whilst phosphorus increased in leaves of shaded V. montana, it increased in stems, pedicels and peduncles of V. chamaedrys. These particular organs of V. chamaedrys exhibit a pronounced elongation response in shade. 4. Shading increased leaf magnesium concentrations and AIs. Species means for both these quantities are inversely proportional to the availability of light in natural habitats occupied by each, which is ranked V. officinalis > V. chamaedrvs > V. montana. 5. The percentage of ash in seeds was ranked V. officinalis > V. chamaedrys > V. montana: a particular balance of mineral nutrients and energy equips each species with proportionately more of the resources that are most likely to limit seedling establishment. Shading decreased the percentage of ash in V. chamaedrys seeds: seeds produced, and probably destined to germinate, in low light have a higher ratio of energy to mineral nutrients than seeds produced in full light. The allocation of ash to seeds was not plastic in V. molitana. 6. Of the three species, roots of V. officinalis contained the highest concentrations of phosphorus and ash (total minerals), and had higher root AIs for all elements but nitrogen. The mineral nutrient characteristics of both established plants and seeds of Y@ officinalis are consistent with its autecology: the acquisition of nutrients and adequate provision of nutrients to seeds are vital in dry, infertile soils. 7. Genotypic differences elucidated by this experiment, such as leaf magnesium concentration, show a gradation between the three species that accords with their individual autecologies and morphological responses to changes in irradiance.

1. The growth responses of Veronica chamaedrys, V. montana and V. officinalis to five levels of irradiance in conjunction with dry, normal and waterlogged soil were investigated using growth analysis. 2. There were no significant differences between species in either relative growth rate (RGR) or unit leaf rate (ULR) and both rates fell with lowered irradiance. Reductions caused by waterlogging were greater than those caused by drought. Water regime had more influence on RGR than did irradiance. 3. Low irradiance caused increases in leaf area ratio (LAR), specific leaf area (SLA) and leaf weight ratio (LWR), although increases in LAR and SLA were suppressed by either soil water deficit or saturation. For both V. chamaedrys and V. montana, waterlogging had the more suppressive effect. Mean SLA in V. officinalis, calculated across the five irradiances, was the same between normally watered plants and those subject to drought. Drought had no effect on LWR in either V. chamaedrys or V. montana, whereas it was increased by waterlogging. In contrast, LWR in V. officinalis remained unaffected by waterlogging but was decreased by drought. 4. Stem and petiole data were combined. The compound weight ratio increased with decreasing irradiance and also with increasing soil water content, although the effect of water treatment was dominant over that of irradiance. 5. Regression analysis demonstrated a positive, linear relationship between root weight ratio (RWR) and irradiance. Root weight ratio also increased with decreasing soil water content and was, in fact, influenced primarily by water treatment. Of the three species, V. officinalis had the highest RWR and showed the greatest reduction in RWR under low irradiance. Overall, waterlogged V. chamaedrys suffered the largest reduction in RWR. 6. Given its low RWR and high LAR and SLA, V. montana would be unable to optimize water use in environments in which low soil water potential was concurrent with high irradiance. In fact, V. montana suffered leaf chlorosis under these conditions. V. officinalis possesses a high RWR but low LAR and SLA and was tolerant of both waterlogging and drought, irrespective of irradiance. Of the three species, V. chamaedrys was least tolerant of waterlogging. At low irradiances the shade responses of V. montana would enable it to maintain a more-favourable carbohydrate balance than V. officinalis, irrespective of water regime.