GHICKWEED. 23 
come smaller, and in winter are sometimes wanting altogether. 
This apetalous* condition is probably due to the fact that in 
winter there are few or no insects to fertilise the flowers, and 
therefore the conspicuous and attractive parts—viz., the petals 
and the little beads of nectar at the bases of the filaments—- 
are frequently reduced, or disappear. Chickweeds are quite 
capable of self- fertilisation—that is to say, that if pollen from 
the anthers of a flower adheres to the stigmas of the same 
flower, the ovules in that flower will be fertilised, and will 
ripen into seeds. And in winter this 1s what very commonly 
happens. But it has been proved by experiments that even 
among flowers which are usually self-fertilised a cross-ferti- 
lisation is advantageous. If, namely, the stigmas receive 
pollen from some flower on a different plant, the seed pro- 
duced by this cross-fertilisation is found to be larger and 
heavier, and to produce larger and stronger plants, than would 
have been the case had the stigmas received their own pollen. 
But it is clear thatin the case of Chickweed only flying in- 
sects, such as sinall bees, flies, moths, or butterflies, could: 
carry the pollen on some part of their bodies, and, as these 
insects are not to be found in winter, the plants seem to 
adjust themselves to their altered conditions, and go on 
producing flowers wanting the very parts so attractive to the 
insects. 
Make transverse and longitudinal sections 
through the ovary, and notice that it is 1- 
celled, and contains numerous ovules on a 
éenttal column, which does not reach much 
more than half-way to the 
summit, This column is in 
reality made up of a great 
number of separate stalks, or 
funiculi, which arise from the 
base of the ovary, and the | Ea, 
form of placentation is called Fig. 22. Trans- Hig. 28. Longi- 
verse section tudinal sec- 
basal. y o_o of ovary of tion of ovary 
3 The ripe fruit is to be Ate EVER ot Clickweed 
found at all seasons of the (mag.). (mag.). 
year, as only a very short 
time elapses between the withering of the flower and: the 
ripening of the seeds. Notice that the pedicels of the flowers 
are nearly erect, but that as soon as the flowers have 
withered they begin to bend and at last hang down: this 
is evidently to let the seeds fall out as goon as they are 
ripe. The sepals remain attached as a covering to the 
Gyan, the walls Sen) of which become thin and dry, 
qi Eiterully Ma nee petals,” 
