NOTE ON THE HISTOLOGY OF GRAIN ROOTS 
Grace A. Dunn 
(Received for publication December 6, 1920) 
In the winter of 1920, Dr. Sophia Eckerson and the writer were engaged 
in a microchemical study of the physiology of the absorption of different 
salts by plants grown in water cultures, especially Zea mays (white dent) 
and Triticum vulgare. The experimentation was carried out in Dr. Rodney 
H. True's laboratories in the U. S. Bureau of Plant Industry, at Washington. 
In this work it was observed that roots of Indian corn and wheat grown in 
solution cultures showed an interesting structural feature that has apparently 
not yet received attention in the literature. Openings appeared in the 
root cortex, the time and place of their appearance varying with the plant 
and with the solution used. No serious study of the causes involved in 
the formation of these openings was attempted, but some histological 
observations were made as to the general manner of their occurrence. 
Hand sections of the roots were used. Since it was necessary to discontinue 
these studies for the time being, this note has been prepared in order to 
present the information which has thus far been gained. 
The seeds were germinated between sheets of filter paper moistened 
with distilled water, and the seedlings were placed in the solutions when 
the roots were 1-3 cm. long. Some cultures were maintained in darkness 
at a temperature of about 18° C., while others were under laboratory 
conditions at a temperature between 17° and 22° C. Tests showed that 
the solution concentration varied considerably during an experiment; the 
solution was not changed during the culture period, 7-14 days. Single- 
salt solutions of Ca(N03)2, Mg(N03)2, KNO3, CaS04, MgS04, and K2SO4 
were employed, each with 0.00024 normal concentration. Also, both plant 
forms were grown in 3-salt solutions containing KH2PO4, Ca(N03)2, and 
MgS04, with a trace of FeP04. Openings were found in plants of both 
species grown in each of these solutions, these openings appearing in the 
corn roots after 3 or 4 days, much sooner than in the case of wheat. They 
appeared in wheat roots, in all the single-salt solutions, after 8 days, de- 
veloping more rapidly in solutions with the calcium salts than in those with 
either the magnesium or the potassium salts. 
As to the openings themselves, when they are first observed they are 
of about the size of the adjoining cortical cells, as shown in figure i, and 
appear like large intercellular spaces formed by a separation of adjacent 
cells in the cortical tissue. In later stages the openings appear larger, 
and there is evidence (at least in the case of corn) that some cells have broken 
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