2091. According to Mr. Hunt's hypothesis, the solar rays produce three distinct classes of phenomena, viz. light, heat, and chemical agency or actinism; and these phenomena, he thinks, are produced by different coloured rays. Thus, he considers that the yellow are the luminous rays, that the red rays produce heat, and that chemical action, or actinism, is produced by the blue rays; and, following up this idea, he thus describes the effects which he supposes the different coloured rays produce upon plants: ï¿½ 'Yellow light, or luminosity, impedes germination, and accelerates that decomposition of carbonic acid which produces wood and woody tissues. Under its influence leaves are small, and wood short-jointed. Red light (heat) carries heat, is favourable to germination, if abundance of water be present increases evaporation (or perspiration), supports the flowering quality, and improves fruit. Under its influence colour is diminished, and leaves are scorched. Blue light (chemical action or actinism) accelerates germination and causes rapid growth. Under its influence plants become weak and long-jointed.'