Appendix E 427 



additional expense is not involved in growing the plants under 



The following suggestive directions may be given to each 

 student : 



Materials. 1. Instruments: tweezers; scalpel; small, sharp- 

 pointed scissors, hand lens, etc. 



2. For covering flowers: Manila bags, waxed paper bags, 

 cheese cloth, etc. Wire labels, stringed tags, fine copper wire 

 or twine cut into short lengths may be used to fasten the bags. 



Preliminary study of plant. 



Before attempting to cross plants, it is necessary to know the 

 structure of the flower to be used. To do this (A) locate 

 all parts sepals, petals, anthers, filaments, stigma, style, 

 ovary; (B) determine whether the flowers are perfect or 

 imperfect; ((7) learn to recognize the "ripe" or receptive 

 condition of the stigma and pollen. 



Technique. 



(A) Emasculation. (Unnecessary where stamens and pistils 

 are borne on different flowers.) For crossing purposes 

 select flowers in which the anthers have not opened. Re- 

 move the anthers with tweezers or scalpel, taking care not 

 to injure the stigma. It may be necessary to remove part 

 or all of the petals in some flowers in order to get at the 

 anthers, but it is best to remove only the anthers, if possible. 



(B) Bagging. After the anthers have been removed, the 

 flower should then be covered with some material, as a 

 manila or oil paper bag, to prevent the entrance of foreign 

 pollen. When the stigma is receptive, remove the covering, 

 pollinate with the desired pollen of known purity, and im- 

 mediately cover again, leaving cover on until fertilization 

 has taken place as indicated by withered or brownish 

 stigma. It is desirable to remove the covering when the 

 cross has "set." 



