436 PROTOPLASM 



is very small, but the claim is made that its presence has been 

 definitely determined in potato, lima bean, peach pit, egg, beef, 

 and human cancerous tissue. The blue color of the flowers of 

 Hydrangea when grown on certain forest and moor soils may be 

 due to the presence of aluminum salts; these may also be artifi- 

 cially added to the soil (though hydrogen may be the responsible 

 element here). The metal has an effect, but it cannot be said to 

 be either beneficial or harmful. 



In General. — R. W. Thatcher has classified into eight groups 

 the elements found in plants. He adds that all the elements 

 known to have any function in plant nutrition occur in the first 

 four orbits of the periodic table. The groups are (I) hydrogen 

 and oxygen, energy-exchange elements; (II) carbon, nitrogen, 

 sulphur, and phosphorus, energy storers; (III) sodium, potas- 

 sium, calcium, and magnesium, translocation regulators; (IV) 

 manganese, iron (cobalt, nickel), copper, and zinc, oxidation- 

 reduction regulators; (V) boron, aluminum, sihcon, arsenic, 

 selenium, functions unknown; (VI) chlorine, fluorine, bromine, 

 and iodine, functions unknown; (VII) cobalt and nickel, functions 

 unknown; (VIII) germaniimi, gallium, and other rare elements, 

 functions unknown. 



The Salt Environment. — Claude Bernard reminded us that 

 the living cell could not be considered apart from its environ- 

 ment. The chief constituent of this environment is water, and 

 the second in importance is its salt content. As far back as 

 1773, Hewson observed that blood corpuscles were destroyed 

 in water but remained normal in salt solution. A century later 

 came the famous experiments of Ringer from which resulted the 

 now much used Ringer solution. 



Two points of view have guided investigators in the selection 

 or preparation of solutions in which to immerse tissues; the one 

 has been along physical and the other along chemical lines. 

 When blood corpuscles are to be studied outside the body, 

 there is no thought of supplying a nutritive solution but only 

 of supplying one that will prevent a collapse in the normal 

 condition of the cell, such as hemolysis (the loss of the hemoglobin 

 by dispersion through the membrane). But when cells are to 

 be grown in laboratory cultures, as are animal tissues or plants, 

 then the first prerequisite is nutrition; physical factors, such as 

 osmotic pressure, receive secondary consideration. Salts may 



