66 GLASS-BOOK OF BOTANY. 
stigma slightly protrudes from the corolla-tube, while the 
anthers are found a long way down the tube. Such flowers 
are popularly called ‘‘pin-eyed.” In the other series the 
anthers protrude slightly from the throat of the corolla, while 
the style is so short that the stigina is placed at a level cor- 
responding with the stamens of the first-mentioned kind: and 
these are known as ‘‘ thrum-eyed.” This peculiarity is named 
heterostylism,* from the varying lengths of the styles in the 
two forms. It has been demonstrated by careful experiments 
that, in order to secure the formation of the finest capsules and 
the most numerous and heaviest seeds, it is necessary for the 
stigmas of either kind to receive pollen from the stamens of 
the other kind, which stand at the same level in the corolla- 
tube. Naturally this is what must take place, for an insect 
in visiting the long-styled form for nectar will get pollen on 
the lower part of its trunk from the stamens far down the 
tube: in going to a short-styled form it will probably leave 
some of the pollen on the stigma, and at the same time get 
some more pollen on the front of its head or the base of its 
trunk, from the stamens at the top of the tube. The latter 
will, in the course of the insect’s visits, be transferred to the 
stigma of a long-styled flower. If the flowers are so protected 
that insects cannot get to them, it is found that they are 
altogether, or almost wholly, unproductive. 
Any other Primula may be examined instead of the Primrose—ey., 
the Cowslip (P. veris), the garden Polyanthus, which is a hybrid of two 
or three other species, the Auricula (P. auricula) or P. sinensis. In all 
these the umbel is much more conspicuously developed than in P. vul- 
garis, but the flowers are almost identical in structure. 
The only New Zealand plant allied to the Primrose is a 
creeping herb—Samolus littoralis— which is common in 
marshy ground near the sea. 
Fig. 118. Samolus ; ; 
longitudinal sec- _ |. } 
tion of ovary(mag.) Fig. 119. Pimpernel ; longt- 
cal, calyx. tudinal section of ovary 
(mag.). pl, placenta. 
Examine the common Pimpernel (Anaga 
ealled also the Poor Man’s Weather-glass, becau 
* Gr, heteros, diverse. 
Fig. 120, Capsule of 
Pimpernel. 
Ilis arvensts)— 
se its flowers 
