1914] Bartlett,— Systematic Studies on Oenothera,— IV 37 
Mendelian. Early in the morning the unopened flower buds of the 
two varieties look very unlike. The material (it seems to be a mixture 
of a sugar and a weak acid) which is excreted by the thin-walled clavate 
hairs of the typical form will have deliquesced, and each hair of this 
type is then tipped by a drop of viscid solution, sufficiently concen- 
trated so that it has a decided taste. In this condition the buds are 
greener than when dry. The buds of var. grisea, on the contrary, 
have no secreting hairs and remain dry and gray. When wet by the 
dew, the droplets condensed on the pubescence have no taste. On a 
dry day the gross appearance of the buds of the two varieties is the 
same but they can be readily distinguished with a hand lens. In 
general, the viscid character of many Oenotheras (Oc. Lamarckiana, 
for example) is due to secretions from the thin-walled clavate hairs 
of the pubescence. The red (or green) tubercles at the base of some 
of the sharp thick-walled granulose hairs seem to have no secretory 
function. 
The photographs of Oe. venusta var. grisea accompanying this article 
were taken under the writer’s supervision in the garden of the Bureau 
of Plant Industry at Glenn Dale, Md., season of 1913. Oe. franciscana 
is being used for genetic studies and plants of the type strain will 
eventually be illustrated in that connection. 
Bureau OF PLant Industry, Washington, D. C. 
EXPLANATION OF PLATES. 
Plate 107. Oe. venusta var. grisea, (above) mature rosette, (below) flowering 
plant. : . 
Plate 108. Oe. venusta var. grisea, inflorescence and details. 
In each figure the reduction may be calculated from the label, which is 
10 em. long. 
