188 MENDELISM 



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 opera- 

 tions. 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 emas- 

 culation 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 



