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OBSERVATIONS UPON THE NEWER BOTANY. 
ByrRON D. HALSTED. 
THE LEAF A LIGHT-RELATED ORGAN, 
Unper life relations it may be an advantage to some that an 
instance be stated even though it be in brief terms. Let us 
take the leaf as it is, one of the three vegetative organs. 
The leaf is divided into three parts—the stalk, stipules, 
and blade. Furthermore, the blade is made up of the framework, 
the pulp, and the skin that envelops all and holds the parts 
together. It has been stated that the leaf is a light-related 
organ, and it will be to the point to consider this relationship. 
It is the pulp that interests us in considering the leaf as 
related to the light, and this is the soft portion lying between 
the upper and lower skin, and supported by the framework. It 
consists of minute cells somewhat loosely placed. 
It is now that the microscope lends valuable assistance, for 
by it it is seen that the cells consist of three parts, the wall or 
sac, the liquid, and the green granular contents. 
It is these minute masses of protoplasm, colored green by 
chlorophyll that interest us ina study of the light relation, for 
it is in these that the energy of motion is transformed into energy 
of position—kinetic into potential. 
Within these chlorophyll granules the energy of the vibrat- 
ing rays of the sun splits up the molecules of water, coming 
from the soil through the roots and stem, and those of the car- 
bonic dioxide from the atmosphere driving off a portion of the 
oxygen. Thus, if we should have six groups of the carbon 
dioxide molecules (6 CO,) and five of water (5 H,O) there 
might be a separation of twelve atoms of oxygen, and the union 
"Remarks following a paper upon Botany for the Secondary Schools, by Dr. J, 
M. Coulter, before the Natural Science Section of the National Educational Associa- 
tion, Washington, D. C., July 1898. 
1898 ] 259 
