134 THE SIGNIFICANCE OF ANTHOCYANINS [CH. 



solution, the temperature in the vessel containing red leaves rose higher 

 than that in the one containing green. 



Stahl's (405) experiments and his criticism of the work previously 

 done in this direction are all included in his paper 'Ueber bunte Laub- 

 blatter.' An account is first given of his experimental work on the 

 method of finding the respective temperatures of red and green leaves. 

 The apparatus used was a thermo- junction with spathulate electrodes 

 which could be buried in the substance of the leaf. The source of light 

 was a gas burner, and sometimes a Leslie cube was used by which dark 

 heat only was obtained. Owing to the size of the electrodes, thick 

 and fleshy leaves were most suitable for use. One of the species 

 employed was an epiphytic orchid, Sarcanthus rostratus. On taking 

 the temperature of both green and red leaves, it was found that the 

 red had a temperature of 1-5 above the green in one experiment, in 

 another of 1-82. Similar results were obtained with the red and green 

 parts of one and the same leaf of Sempervivum tectorum. Though more 

 difficult to manipulate, some thin-leaved plants were used with similar 

 results; for example, a difference of temperature of 1-35 for Begonia 

 heracleifolia var. nigricans, 0-22 for Pelargonium peltatum and 0-14 for 

 Tulipa Greigi. A rise in temperature of red leaves over green was 

 also obtained when the Leslie cube was used. In addition, other 

 investigations were made using coco-butter instead of the thermopile. 

 The melting-point of the butter was raised by mixture with beeswax, 

 and was then spread in a liquid condition as thinly as possible on the 

 under surface of the leaf. When the butter was set, the upper leaf- 

 surface was exposed either to the sun's rays or to the heat of the Leslie 

 cube. The butter was found to melt more rapidly, and to a greater 

 degree, on red leaves, or parts of leaves, than on green. 



Stahl then proceeded to apply these results to cases which have 

 been discussed by previous investigators. With regard to Kerner's 

 experiments on Linum and Satureja in the Tyrol, which we have already 

 noted, Stahl suggests that it is not from lack of protection of chlorophyll 

 that the flax suffers, but from the low night temperature, against which 

 it would be protected were it able to form anthocyanin with the resultant 

 raising of temperature. Stahl proposes that the additional experiment 

 should be conducted of covering up the Linum by night. If then the 

 plant is still unable to survive, Kerner's view is more feasible. In 

 general, also, with Alpine vegetation, Stahl is of the opinion that the 

 red leaves and stems take a higher temperature than the green, and 

 thus in a wider and more general sense than Pick he says "in dem 



