ADVANTAGES OF KNOWLEDGE OF VEGETABLE PHYSIOLOGY. 189 



cause the green chlorophyll to appear, but unequally so. The 

 use of the chlorophyll granules is to decompose carbonic acid gas 

 absorbed from the atmosphere, of which it forms, on the average, 

 about one twenty-fifth part per cent. From this the carbon is 

 retained for making tissues, while the oxygen is liberated. It is 

 found that only certain parts of the solar spectrum are specially 

 concerned in this process, though probably others assist. Such 

 are some of the brightest parts of the spectrum, as well as some 

 in the blue portion; but any specially coloured glass taken alone 

 is injurious to plant life. The ill effects can be seen by growing 

 Lettuces or other plants in frames under coloured glasses, when it 

 will be found that the red and yellow glass tend to elongate the 

 stem, as takes place in the dark. Green glass proves to be the 

 very worst colour of all. As examples of a mistaken view, Mr. 

 Decimus Burton constructed the Palm-house of Kew with a glass 

 slightly tinted green, according to Dr. Daubeny's advice. This 

 was with the idea of reducing the glare. Fortunately the tint 

 is so slight as to do no harm if it does no good. It proved 

 otherwise with the Fern-houses at Kew. The green glass of a 

 deeper tint with which the Ferns there were covered, proved to be so 

 injurious that it has been replaced with ordinary transparent 

 glass. The fact is that plants have been attuned by Nature to 

 the whole body of light, and it is only a question of its being 

 either too intense or insufficient. If, therefore, the light has to 

 be subdued, it must be done by some white material that reduces 

 the amount by reflection, or otherwise, without decomposing the 

 light itself. Such are the suggested practical results from 

 physiological experiments. 



Transpiration, though carried on by the colourless living 

 protoplasm everywhere throughout the plant, is intensified by 

 green chlorophyll, and like assimilation is largely dependent on 

 certain rays. It must be distinguished from evaporation which 

 results from heat. All dead and moist substances will evaporate, 

 but only living plants transpire. As this function is most 

 active when there is much foliage, it is easy to see how un- 

 desirable it is to transplant herbaceous plants when in full 

 vigour, as the check to absorption by the roots can only be 

 overcome by supplying a superabundance of water until the 

 plant has established itself. 



Floiuers. — Coming to the reproductive organs, the process of 



