848 
Journal of Agricultural Research voi. xxvn,No. u 
CHEMICAL METHODS 
The chemical determinations of the various elements with the exception 
of sulphur and phosphorus were made, in general, according to the 
methods for the analysis of plant material recommended by the Associa¬ 
tion of Official Agricultural Chemists. The sulphur and phosphorus 
were determined after the following method described by Latshaw (7). 
One to two grams of the sample, or a sufficient amount to give a precip¬ 
itate of not less than 30 mgm. of barium sulphate, were weighed into a 
250 cc. low form Pyrex beaker. To this were added 7.5 cc. of a magnesium 
nitrate solution, 3 care being taken that all the material was brought in 
contact with the solution and heated on an electric hot plate (180° C.) 
until no further action took place. The beaker was transferred while 
hot to an electric muffle and allowed to remain at low heat (muffle not 
showing any red) until the charge was thoroughly oxidized and no black 
particles remained. If necessary, the charge was broken up and again 
returned to the muffle. The beaker was removed from the muffle and 
allowed to cool. Water was added, then hydrochloric acid in excess, the 
solution brought to a boil, filtered and washed thoroughly. This solution 
was then diluted to 200 cc., heated to boiling, and a 10 per cent barium 
chlorid solution added in small quantities until no further precipitate was 
formed. The boiling was continued for five minutes, after which the 
liquid was allowed to stand for five hours or longer in a warm place. 
The liquid was then decanted on an ashless filter or a tared Gooch crucible 
previously heated, the precipitate treated with 15 to 20 cc. of boiling 
water, transferred to the filter and washed free of chlorids with boiling 
water. The precipitate was ignited and weighed as barium sulphate. 
The filtrate obtained in the sulphur determination was evaporated to 
75 cc. and the phosphorus determined by the method recommended by 
the Association of Official Agricultural Chemists. 
The figures in the various tables representing the amounts of oxygen 
include the oxygen obtained by the usual procedure in organic analysis 
plus the oxygen that was a part of the various mineral elements of the ash 
when they were converted to their oxids. The figures thus represent 
the oxygen of both organic and inorganic combination. 
The determinations were all made in duplicate or triplicate and when¬ 
ever any striking differences appeared in the analysis of the individual, 
plants a careful redetermination was made to verify the results. Any 
marked differences recorded in the composition of the same organ of the 
different plants are due to individual variations and not to discrepancies 
in the chemical methods used. 
DISCUSSION OF EXPERIMENTAL DATA 
In order to determine the variation in the composition of the different 
plants and their organs a separate analysis was made of the leaves, stem, 
and grain of each of the five plants. A separate analysis was also made of 
each of the five root systems. Determinations were made for carbon, 
oxygen, hydrogen, nitrogen, phosphorus, potassium, calcium, magnesium, 
sulphur, iron, silicon, aluminum, chlorin, and manganese. The amount 
of each of the elements that compose the leaves, stem, and grain of each 
of the five plants is expressed in percentage of dry weight and in the 
actual amount, in grams, in Table III. 
8 Made by dissolving 320 gm. of calcined magnesia in nitric acid, avoiding an excess of the latter. Cal¬ 
cined magnesia is then added slightly in excess, the solution boiled, filtered from the excess of magnesia, 
iron aluminia, etc., and diluted to two liters. 
