g
the ovules enlarge to form the pod. When this, the normal mode of
fertilisation, takes place, the flower is said to be SELFED.

In crossing, it is necessary to emasculate a flower on the plant chosen to
be the female parent. For this purpose a young flower must be taken in
which the anthers have not yet burst. The keel is depressed, and the
stamens bearing the anthers are removed at their base by a {188} pair of
fine forceps. It will probably be found necessary to tear the keel slightly
in order to do this. The pistil is then covered up again with the keel, and
the flower is enclosed in a bag of waxed paper until the following day. The
stigma is then again exposed and dusted with ripe pollen from a flower of
the plant selected as the male parent. This done, the keel is replaced, and
the flower again enclosed in its bag to protect it from the possible
attentions of insects until it has set seed. The bag may be removed in
about a week after fertilisation. It is perhaps hardly necessary to add
that strict biological cleanliness must be exercised during the fertilising
operations. This is readily attained by sterilising fingers and forceps
with a little strong spirit before each operation, thereby ensuring the
death of any foreign pollen grains which may be present.

The above method applies also to sweet peas, with these slight
modifications. As the anthers ripen relatively sooner in this species,
emasculation must be performed at a rather earlier stage. It is generally
safe to choose a bud about three parts grown. The interval between
emasculation and fertilisation must be rather longer. Two to three days is
generally sufficient. Further, the sweet pea is visited by the leaf-cutter
bee, _Megachile_, which, unlike the honey bee, is able to depress the keel
and gather pollen. If the presence of this insect is suspected, it is
desirable to guard against the risk of admixture of {189} foreign pollen by
selecting for pollinating purposes a flower which has not quite opened. If
the standard is not erected, it is unlikely to have been visited by
_Megachile_. Lastly, it not infrequently happens that the little beetle
_Meligethes_ is found inside the keel. Such flowers should be rejected for
crossing purposes.

* * * * *

{191}

INDEX

_Abraxas grossulariata_, 99
"Acquired" characters, 14
Adaptation, 143
Agouti mice, 50
Albino mice, 50
Albinos, nature of, 53
_Amauris_, 14