THE INFLUENCE OF SHADING AND OF SOIL TYPE ON THE GROWTH OF GALEOBDOLON LUTEUM.

(1) British populations of Galeobdolon luteum (Lamiastrum galeobdolon) are almost all of the tetraploid (4n = 36) subsp montanum. Populations of this taxon growing in different environments, with a very vaned range of plant associates, show marked differences m such features as stolon production, leaf width, chlorophyll content, and the extent of flowering and fruiting. (2) Investigations of clones collected in Shropshire show that many of these differences are environmentally induced, although some are genetic in origin. (3) In studies of phenotypic plasticity, plants of clonal and of seedling origin were grown in the open and beneath shade-screens in cold frames which at midday received approximately 70% (A), 27% (B) and 6% (C) of the light available to the open treatment (O). Growth analysis showed that specific leaf area (SLA), leaf area ratio and fresh weight dry weight ratio were always highest in the most heavily shaded treatment Within the light ranges investigated, chlorophyll contents per unit dry weight of leaf were directly related to degree of shading Galeobdolon grew much better under Treatment A (70% light = 30% shade) than Oxalis acetosella did in similar experiments Total leaf area and stolon length were highest in Treatment B (73% shade), in which maximum leaf width was greater than that in the less shaded treatments (A and O). By the end of the first season total mean dry weight of seedlings in Treatments A and B was considerably greater than that in Treatment O (full light) and much higher than that in Treatment C (94% shade). Plants in this very densely shaded treatment differed from the others in showing a considerable increase m dry weight during the winter Well established plants in all treatments except the deepest shade (C) flowered well. (4) Shade leaves of Galeobdolon have better developed funnel-cells (palisade cells tapering strongly towards the spongy mesophyll) than do sun leaves are much thinner and have lower stomatal frequency... [ABSTRACT FROM AUTHOR]