1904] BRIEFER ARTICLES 145 
In accordance with the statements of Haberlandt and Schwartz, 
Elodea roots, though hairless in water, produce hairs when growing in 
the substratum of the aquarium, even if the material be ground quartz. 
Microscopic examination has shown thus far that the average length of 
epidermal cells of roots in the substratuin is less than that of epider- 
mal cells of roots in the water. The presence of hairs seems to be 
related, therefore, to the length of the cells rather than to superficial 
contact. Insupport of theideathat contact of the epidermal cells with 
solid bodies does not appear to be a stimulus for hair production, may 
be cited certain instances where roots of seedlings grew against the 
sides of a glass vessel; in this condition there was a marked tendency 
for the suppression of hairs along the region of contact. Also seed- 
lings grown in saturated sand or garden soil show a diminution or 
even absence of hairs, as previously indicated by Persecke. 
That temperature has an effect, though possibly an indirect one, 
upon hair production is evidenced by roots of corn and wheat seed- 
lings showing a tendency to omit the hair zone when growing rapidly 
in warm water. 
From the foregoing statements there appears to be a relation 
between the production of root hairs and the elongation of the cell ; 
whatever has a tendency to increase the elongation also tends to sup- 
press the development of hairs, “water etiolation” being especially 
important in this connection in soil roots. In two cases of decapitated 
~ sunflower seedlings the water etiolation of the periblem and epidermis 
was apparently so great that the poorly nourished, deeper lying ple- 
rome was not able to keep pace with it and hence split transversely in 
several places. ‘he frequently noted decrease of hairs in etiolated 
conditions of the aerial parts of plants, whether from darkness or 
moisture, supports this view. 
The production of hairs coincident with slow growth above men- 
tioned is net thought to be due to excess of nourishment, as sup- 
posed, but merely to the tendency of the cells to grow transversely 
rather than to elongate longitudinally. This is supported by the con- 
dition of affairs in Lycopodium and Isoetes, and by Leavitt’s associa- 
tion of root hairs of Azolla with cells which do not elongate. The 
root hair problem therefore, appears, to resolve itself in large part into 
the search for the causes of arrested growth or the elongation of cells. 
Other references, illustrations, and conclusions will be reserved 
until the work is more complete. — LAETITIA M. Snow, Aull Botanical 
Laboratory, The University of Chicago. 
