to the Plant Cell. 
5 1 1 
stained and converted into permanent preparations for more detailed study. 
The same was true of the prothalli of the ferns employed. The root tips 
of young chlorophyll-bearing plants which were always grown in, water 
cultures were studied only after being fixed, sectioned and stained. The 
filaments of Basidioholus yielded little when studied in the living condition, 
but when fixed and stained they permitted of accurate study with the 
higher powers of the microscope. 
With each plant experiments were conducted which were designed to 
show the role of certain elements in the physiology of the cell. This was 
accomplished, in most cases, by using a series of solutions which lacked, in 
turn, one of the essential elements ; the missing radical being replaced by 
a non-essential and non- toxic (at least at the concentration employed) 
radical. After living in the deficient solution for a varying length of time, 
depending both upon the nature of the plant employed and the purpose 
of the experiment, the plants were studied microscopically and compared 
with the cells of a like plant which had lived for a similar time and under 
exactly similar conditions in a complete nutrient solution. 
2. Preparation of nutrient solutions. 
In preparing the nutrient solutions, little difficulty was experienced in 
obtaining chemically pure salts of the standard chemicals. 
A supply of pure non-toxic distilled water was not, however, always 
easy to obtain. Ordinary distilled water is seldom suitable for physiological 
work, because it contains traces of the metals which compose the distilling 
apparatus. Usually copper is employed in some form in the construction of 
the apparatus, and the traces of this metal in the distilled water have been 
recognized as sources of error for some time. The use of block tin apparatus 
reduces the amount of metallic material in distilled water to practically nil. 
Apparatus of glass was used in most of the redistillation which I performed, 
but since the alkali silicates are quite soluble, the water obtained from such 
apparatus contained more or less alkali salts. 
Alkaline permanganate was usually added to the distilling flask ; and 
a satisfactory grade of distilled water was usually obtained. While the 
experimental work was still in progress, a method was devised by 
Livingston (’ 07 ) which gives a non-toxic distilled water. By the use 
of a finely divided solid, substances are removed by absorption which are 
extremely difficult to remove by distillation. To obtain such physiologi- 
cally pure water, I used freshly prepared ferric hydroxide, as an absorbing 
agent, which was made by adding ammonium hydroxide to a hot solution 
of ferric chloride so long as a precipitate was formed. The excess of 
ammonium hydroxide was boiled off, and the ferric hydroxide was filtered 
out. The precipitate was thoroughly washed on the filter with hot water. 
About 350 cc. of the moist ferric hydroxide was added to a bottle con- 
