THE AMERICAN BOTANIST. 
he found the whole valle3^ of the Wachan so filled with th^ 
scent of the vine flowers that it seemed impossible that" 
they could be far off, yet the nearest vines were 300 yards 
from the boat. The honeybee and many beetles have been 
collected on the flowers. Various exotic species of the 
nightshade family and some Brazilian orchids possess^ 
large green flowers. They are strongl}^ scented in the 
evening and are attractive to moths. ' 
There are 790 yellow flowers in northeastern America, 
which var3^ greatly in size and form. Usually they are 
wheel-shaped as in the buttercups and five-fingers ; but 
not infrequently the^' are very irregular in form, as in the 
pea and figwort families where the corolla bears a more 
or less fancied resemblance to butterflies and the heads of 
reptiles. As a wdiole, however, they are much less special-- 
ized than red or blue flowers. Highl}^ modified yellov^ 
flowers usually exhibit great persistency of the primitive 
yellow, and little tendency to vary in color. In the gold-' 
enrods the individual flowers are ver^^ small and conspictt-^- 
ousness is gained by their aggregation in dense clusters^ 
The bright yellow color of the flowers render them visible 
in the evening as well as by day, and as the temperature 
of the inflorescence at night is several degrees above the 
surrounding air they sometimes serve as a refuge for* 
insects. 
It was a few years ago believed that the drone flies 
especially admired yellow, flowers. Because they were 
observed to hover over the bright blossoms of buttercups' 
and marsh marigolds it was thought that they were 
admiring the shining yellow surface. But there is not a' 
particle of evidence that this is so. Their behavior is 
rather due to their habit of flight, and Plateau has 
observed them poising on the wing before buds and sticks 
and even the human finger. 
The yellow color of autumn leaves and of most flowers 
is caused by a pigment called carotin, familiar to everyone 
in the root of the carrot. It always occurs in solid 
granules called plastids, and is insoluble in water but 
