HOW TO DISSECT A FLOWER. 
145 
insertion of the stamens in the tube of the corolla is just op- 
posite, in each instance, to one of the lobes of* the corolla. 
Usually the stamens are alternate with the petals, or lobes of 
the corolla ; hence this observation becomes of importance. 
The centre of the flower is occupied by the 'pistil. In the 
primrose, a long slender filament with a pin-like head stands in 
the centre. When the stamens are half-way up the tube, they 
surround this filament, and the head reaches to the orifice of the 
tube. When the stamens are at the mouth of the tube, the 
head of the pistil, which in this flower is the stigma^ only 
reaches partly up the tube, or as high as the place occupied by 
the stamens in the other form. If the pistil is traced down- 
wards, it will be seen to originate from the top of the ovary. 
Thus the pistil consists of a stigma which forms the pin-shaped 
head, a style or filament which supports the stigma, and the 
ovary from whence it springs (fig. 8). As seen by a pocket lens 
the stigma will present a minutely hairy appearance (fig. 9), but 
the one-inch objective of a microscope shows that its surface 
consists of a multitude of delicate clavate hairs (fig. 10). 
Finally, the ovary must be examined, and both transverse and 
longitudinal sections made. These sections prove in the present 
instance that the ovary is one-celled, and that a central prolon- 
gation of the axis supports the ovules. In a transverse section 
this central placenta occupies the centre of a circle of ovules 
(fig. 12). In a longitudinal section, it is manifest that this 
placenta does not pass through the ovary, so as to be continued 
in the style, but stops short, and the ovules are produced at its 
apex as well as around it (fig. 11)# This axile placentation is 
very important, and would lead to a suspicion of the natural 
order to which the plant belongs in the absence of all other 
characters. The ovules themselves are very pretty objects 
under a one-inch objective, having a minutely granulated surface 
(fig. 13). The relative position of the ovary is another very 
important feature. In some plants the calyx is adherent to the 
ovary, and the corolla and stamens are attached to the top of the 
ovary. In such instances, the ovary is said to be hiferior. In 
other plants the calyx is free from the ovary, and springing 
from beneath it the ovary is superior. The primrose has a 
superior ovary (fig. 14). 
From the foregoing examination, therefore, w^e learn that the 
primrose has a tubular five-angled calyx, a regular monopetalous 
corolla, tubular at its lower portion, with five spreading lobes ; 
five stamens inserted in the tube of the corolla, opposite to its 
lobes ; a superior one-celled ovary, with a free axile placenta, 
and numerous ovules, and a capitate stigma. These are charac- 
ters belonging to the genus Primula of the natural order 
PrimulacecB ; and of this genus the primrose is a species. 
