CLEISTOGAMOUS FLOWERS. 
1 77 
point raised a little (i-i-J mm.) above the edge. A dense cloth¬ 
ing of slender hairs obscures the details of the buds until they are 
separated by the elongation of the internodes. Only a few of 
these hairs are indicated in the drawings. No hairs were observed 
on the youngest parts, but were first seen when the sepals are 
elongating to enclose the flower rudiments, at which stage they 
terminate in a tuft of the hairs; these become less abundant as 
the distance from the tip of the sepal or stipule increases.* 
Maryland Agricultural College, 
College Park, Md. 
CLEISTOGAMOUS FLOWERS AND THE THEORY OF 
ADAPTATION.f 
Cleistogamous flowers (those in which pollination takes place 
without the corolla unfolding) have been studied and described 
by many authors, so that the morphology of many of them is well 
known; but attempts at explaining them are not so satisfactory. 
The prevailing theory accounts for them as being an adaptation 
for securing pollination when insects cannot be relied upon. 
Of “ adaptation ” in general there are two theories: 
1. Indirect adaptation, or that resulting from the elimination of 
useless characters through the operation of “ natural selection.” 
That is, there is no direct relation betweeen the adaptive characters 
and the conditions to which they are adapted. 
2. Direct adaptation, or that resulting from the operation of 
external (or internal) conditions. Of this, various interpretations 
are possible. 
With some botanists this latter theory, that of direct adapta¬ 
tion, involves even a psychological factor. Thus, Naegeli says: 
“ Necessity acts as stimulus ” in bringing about adaptive changes. 
Another declares that plants (or animals) have the power to 
vary in a useful manner, according to the external conditions. 
* Prepared for the Philadelphia meeting American Association for the 
Advancement of Science, Section G, December 27-28, 1904. 
t K. Goebel, Biol. Centralb. 24: 673-697, 737-753, 769-787, November, 
December, 1904. 
