194 BOTANICAL GAZETTE [SEPTEMBER 
was noticed with O. Lamarckiana near Hilversum) “ may perhaps be,” 
says DEVRIEs, “one of the conditions for the appearance of a mutable 
period.”* The number of new forms that have arisen and been 
detected by DrEVriEs in the genus Oenothera since his discovery 
of the mutating O. Lamarckiana at Hilversum in 1886 is already : 
considerable. ; 
The following description of the forms O. Lamarckiana, O. biennis, . 
laeta, and velutina represents in each case the average state of affairs 
as shown by a great number of examined specimens. 
O. Lamarckiana is an erect, strong plant. Its stem is cylindrical, 
I-I.5 cm. in diameter, 1.5 or more meters in height, and sparsely 
covered with coarse hairs. Some of the hairs on the stems are glandu- : 
lar. The main stem is more or less branched at the top, and also has : 
a tendency to produce smaller branches at the bottom when it grows 
in an open situation. All of the secondary branches may produce | 
flowers. : ; 
The leaves are somewhat broadly lanceolate, dark green, their 
margins distinctly dentate, and the lower ones strongly petioled. 
Both the upper and the lower surfaces, especially in the adult forms, 
are conspicuously undulated or wrinkled, and only slightly pubescent: 
In order to get buds showing as great uniformity as possible, they 
were chosen just before they were ready to open. The buds of 0. 
Lamarckiana are the largest of any of the three forms mentioned, 
being about 5.5 cm. in length, about 1 cm. broad near the base, and 4 
tapering slowly upward to a width of about 2 mm. at the top. They 4 
are slightly pubescent. This pubescence of the buds of all the three ‘ 
forms studied consists of two kinds of hairs, a small, thin-walled, 
cylindrical hair, and a larger, thick-walled, pointed one. In Y- La 
marckiana both of these hairs are much larger than in any of the 
other forms of Oenothera to be described, and especially is this 
true of the pointed hairs. The buds are almost circular in cross 
section. 
The flowers are large and bright yellow, and arranged rather 
closely together in a broad spike. Each flower is subtended by # 
sessile bract and stands singly. The ovary is partly glandular 
pubescent, and the four lanceolate sepals are strongly reflexed, $°* 
4 DeVries, Huco, Mutationstheorie 1: 152. 
