68G 
Cross-fertilisation of Cereals. 
are perfect, and their pollen grains are scattered, before the 
stigmas of the female flowers on the same plant are ripe and fitted 
to receive them. The pollen grains are consequently carried by 
the wind to other plants which are more advanced, and the 
stigmas are fertilised by the pollen of later flowering plants. In 
some monoecious grasses the stigmas are first ripe, and cross-fer- 
tilisation is equally secured ; while in others the two kinds of 
flowers are ripe at the same time, and fertilisation by the flowers 
of the same plant is favoured. 
In the vast majority of grasses each flower contains both 
stamens and pistil, though among them we also find modifica- 
tions for securing cross-fertilisation. In the two well-known 
pasture grasses, foxtail and vernal grass, the stigmas are pushed 
out beyond the glumes of the flower some time before the open- 
ing of the flower and before the escape of the pollen grains ; 
and as the stigmas remain receptive of the pollen for only a 
short time, they must be fertilised by pollen grains from the 
flowers of other plants which are more advanced. 
The stamens and pistils are, however, generally ripe at 
the same time in grasses, and thus obviously favour self-fertilisa- 
tion ; though, as the anthers contain a large quantity of pollen, 
which is ejected into the air, cross-fertilisation is not excluded. 
A most complete case of self-fertilisation is found in barley. 
Here the pollen escapes from the anther, and is received on 
the moist stigma before the flower opens, and while the ear 
is still within the sheath. When the stigmas are pushed out 
beyond the scales of the flower they are dead. The quality of 
our barley crops sufficiently proves that cross-fertilisation is not 
necessary in all grasses for the production of large and vigor- 
ously germinating grains. 
The fertilisation of the ovules in wheat takes place at the 
time when the flower is ripe and suddenly expands. The very 
short time during which the flower remains open, being not 
longer than a minute or so, makes it difficult to observe with 
care the operation, and has led to very different opinions as to 
what actually takes place. The observations of Francis Bauer, 
as recorded in his drawings, the engraving of which from a pre- 
vious volume of the Journal 1 is here reproduced, show the anthers 
already burst, and some of the pollen grains discharged before 
the flower naturally opens, for the stalks or filaments of the 
anthers are not yet elongated (7 and 8, fig. 1), and the pollen 
grains are already adhering to the divisions of the feathery 
stigma (12 and 13, and the more highly magnified branch, 
Journal R.A.S.E., 3rd iSeries, Vot. III., 1892, p. 97. 
