136 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
2. The leaf. The biternate leaf is regarded as representing the form from which the 
triternate leaves of southern species as well as the simply ternate ones of a few alpine 
species have been evolved. 
3. The presence or absence of indument. When quite universally present, pubescence 
undoubtedly shows specialization. 
4. The petals. Since we must consider these organs to be greatly modified stami- 
nodia, developed from structures similar to the large petal-like organs of some species 
of Isopyrum and Clematis which bear at their bases a small depression in which nectar 
is secreted, it is evident that the large, well-developed laminz as well as the short 
spurs are more primitive than the short or obsolete laminze and long spurs. 
5. The posture of the flowers. The nodding condition of the flower seems to be more 
primitive, for the modern species at least, than the erect position, since the flowers 
of otherwise more primitive plants are nodding while the flowers of otherwise more 
specialized forms are erect. It is also suggestive that the nodding condition is uni- 
versal in the bud. 
6. The color of the flowers. The modern species of Aquilegia seem to have been 
developed from species having blue flowers. These seem first to have given rise to 
white-flowered, these to yellow-flowered, and these finally to red-flowered species. 
7. The habitat. Aquilegia evidently was originally a genus of cooler habitats, and 
an advance into warmer regions is in itself an indication of specialization, inasmuch 
as the less specialized forms structurally are those that live in cool regions and the more 
specialized structurally those that live in the more arid, hotter habitats. An advance 
into arctic conditions (on mountain tops) is also an evidence of specializing adaptation. 
The species of Aquilegia group themselves into three quite distinct sections, which 
I have termed Cyrtoplectrae, Rhodanthae, and Macroplectrae. The first is charac- 
terized by biternate leaves, small, blue or white, nodding flowers, large, dilated 
laminz, short, usually hooked spurs, mostly included stamens, and short styles. The 
second by biternate or triternate leaves, larger, occasionally yellow but usually red, 
nodding flowers, short or nearly obsolete lamine (except in A. flavescens), rather 
long, stout, and mostly straight spurs, exserted stamens, and long styles. The third 
section, Macroplectrae, possesses biternate or triternate leaves, large, erect, blue, 
white, or yellow flowers, large and dilated laminz, very long, slender, straight spurs, 
exserted stamens, and styles of medium length. 
Cyrtoplectrae is the section least conspicuous in America, being represented (so far 
as now known) by only three native species, these local at high altitudes in the Rocky 
Mountains from Colorado into Canada. If we are to assume that the genus had its 
genesis in America, as seems likely, we must consider this section to be the oldest of 
the three, since it alone has spread through the temperate portions of the northern 
hemisphere. It also contains more primitive characters than do the other sections, 
and so may be thought of as representing more nearly the ancestral type of Aquilegia. 
There are in the section Rhodanthae two fairly distinct lines of development, one 
group characterized by A. formosa of the Pacific coast and the other by A. canadensis 
of the eastern United States and Canada. The first contains the species formosa, 
flavescens, tracyi, etc., and is characterized by the rather short spurs, the short or 
almost obsolete laming, and the large, horizontally spreading or reflexed sepals 
which often equal or exceed the spurs in length. This group is connected somewhat 
with the section Cyrtoplectrae by the species flavescens which has small, yellow flowers, 
short and often hooked spurs, and well-developed lamin. In the second group we 
find the most highly developed fiowers of the section in the species A. skinneri of 
Mexico. In this plant the blossoms resemble superficially those of the section 
Macroplectrae and, judging from the length of the spurs and the lighter color of the 
flower, are pollinated differently from those of most other species of this section, i. e., 
by moths instead of humming birds. 
