PHYSIOLOGY. O18 
nerative organ is formed. ‘This is again of a two- 
fold kind. Either the male parts are formed per- 
fectly, before the female parts unfold themselves, 
which he calls Dichogamia androgyna; or it is the 
reverse, the female parts being first formed. ‘This he 
styles Dichogamia gynandra. Homogamy is, when 
both parts of generation are formed in a herma- 
phrodite flower, exactly at the same period. 
Now, in a hermaphrodite flower, when Dicho- 
gamy takes place, impregnation cannot naturally 
happen without intermediate means, by which both 
organs of generation may be brought near each 
other. Linné thought that the wind performed this, 
but there are few plants where wind could do it, as 
most flowers have such a shape as would rather im- 
pede the access of the wind than favour it. Koel- 
reuter first pointed out that many insects serve this 
purpose, and Mr Sprengel had fortunately leisure 
and patience enough to look at, and to witness the 
manner, in which insects proceed in completing the 
impregnation of plants. 
He found that various species of bees, and other 
flying insects, perform this important office; and 
he even observed, that some flowers had their. pe- 
culiar imsects, which alone visited it. His obser- 
vations on this subject are indeed very numerous. 
Those insects, it is true, do not visit the flower on 
purpose to impregnate it, they only seek after the 
sweet juice which exudes from it. Their hairy body 
becomes covered with the pollen, and, whenever they 
visit another flower of the same species, the pollen 
as rubbed against the stigma, and impregnation is 
4 the 
