FERTILIZATION OF FLOWERS BY INSECTS. 281 
Cucurbitacese. Here it is obvious that the transfer of pollen by 
means of insects is rendered absolutely indispensable. In other 
plants, as in Cerastium arvense, the Umbelliferæ and Composite, 
although both sexes are united in the same flower, yet they are 
not developed contemporaneously ; wherefore it is equally neces- 
sary for insects to transfer the pollen from one flower to another. 
Finally in many other plants the flowers are formed and disposed 
in such a way that the transfer of pollen by the agency of insects 
is greatly favored and frequently even rendered necessary 
From among the great number of floral arrangements which 
render heteroclinous impollination necessary, and which have been 
brought to light by the researches of Darwin, Hildebrand, Delpino 
and my brother Fritz, I will mention two which not long since 
ppeared sufficiently enigmatical, which enigma, however, has 
recently been solved by direct observation of the indi ting 
insects; I mean the floral arrangements of the Orchis of our 
meadows, and Cypripedium Calceolus. 
Orchis Morio, mascula, latifolia and maculata have a spur in 
their flowers in the cavity of which no honey is found. This 
absence of honey is a phenomenon without parallel in the vegetable 
kingdom. Sprengel on that account called them plants with false 
nectaries (Scheinsaft pflanzen), imagining that the insects which 
visit them are deceived by the odors, colors and form of the spur 
into inserting their heads into the fauces of the flower with the 
expectation of finding honey. He was never able, however, to 
observe how the fecundating insects conduct themselves in the 
flowers of these Orchises. He observed, indeed, frequently, masses 
of pollen displaced and sticking upon the stigma, and occasionally 
came upon dead flies in the flowers, whence he concluded that flies 
are the fecundators of these plants. Nevertheless, the floral ar- 
rangement of the Orchises remained somewhat mysterious to him. 
“It is inconceivable to me,” he says on page 404 of his work, 
“how it is that such flowers produce no honey, when, as it seems 
to me, it would be much better for them to produce it with a view 
to enticing flies to visit them repeatedly and fecundate them.” 
It is clear that Sprengel himself was conscious of not having 
completely deciphered the enigma. Darwin, too, as we read in his 
work on the Orchids, never succeeded in surprising insects in the 
field Orchis, although he had observed’ them diligently not less 
than twenty years. Nevertheless, he proceeds to expose in detail 
