LIGHT AND LIFE. 109 
and that those of the greatest illuminating power are also 
those which act with most energy on plants, Prillieux un- 
dertook to examine what influence will be exercised on 
plants by rays different in color, but known to be equal in 
intensity, and whether this influence differs in the case of 
different colors, or is the same, provided they do not vary 
in illuminating power. The long and conscientious re- 
searches of this experimenter led him to the conclusion 
that rays of different colors act with equal force on the 
green parts of plants, and produce an equal release of gas, 
when they have the like luminous intensity. He holds 
that all luminous rays effect the reduction of carbonic acid 
by vegetables in proportion to their illuminating power, 
whatever their refrangibility may be. If the yellow and 
orange rays are more active in this respect, it is because 
their luminous glare is much greater than that of the ex- 
treme rays. 
The luminous rays also promote the production of green 
tissue, the green matter of all vegetables. Gardeners 
blanch certain plants by raising them in the dark. They 
thus obtain plants of a pale yellow, spindling, without 
strength or crispness. They are attacked by a true chloro- 
sis, and waste away, as if sprung from barren sand. The 
sun also aids the transpiration of plants, and the constant 
renewal of healthy moisture in their tissues. On failure 
of the evaporation of moisture, the plant tends to grow 
dropsical, and its leaves fall, from weakness of the stem. 
This love of plants for light, which is one of the most 
imperious needs of their existence, displays itself also in 
other interesting phenomena, which show that solar rays 
are, in very truth, the fertilizer that produces color. The 
corolla of vegetable species growing at great heights on 
mountains has livelier colors than that of species that spring 
in low spots. The sun’s rays, in fact, pass more easily 
through the clear atmosphere that bathes high summits. 
