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. 
Flowers .—Coming to the reproductive organs, the process of 
F 
