PEDIGREE-CULTURE. 25 



fertilization as may be required by the particular experiment 

 in hand, (b) the protection of the pollen to be used from 

 mixture with pollen from unknown sources, (c) the convey- 

 ance of the pollen to the stigma of the desired mother-plant, 

 and (d) the continued protection of the latter until the possi- 

 bility of its accepting pollen from any other source is past. 

 In carrying out this program each individual case will re- 

 quire special refinements of technique which can only be de- 

 rived by a study of the peculiarities of the particular species 

 under experimentation. For example, plants which, like 

 Helianthus aiinuus and all dioecious species, cannot fertilize 

 themselves, will not require the removal of the stamens, and 

 this fact greatly simplifies the technique in some cases which 

 would otherwise present peculiar difficulty. 



When self-fertilization Is possible, the conduct of "pure- 

 line" experiments Is peculiarly easy, the only important re- 

 quirement being the exclusion of foreign pollen. On the 

 other hand, if the experiment with self-fertilizing material 

 requires that a cross be made, the stamens must be removed 

 from the plant chosen as the mother, before the anthers 

 dehisce, the time at which this must be done being different 

 in different plants, according to the relative precocity of 

 stamens and pistils. In Oenothera it Is necessary to castrate 

 24 hours in advance of anthesis, while In strongly proter- 

 ogynous flowers the anthers may be remov^ed at the time of 

 pollination. Both the stigmas and the pollen must be pro- 

 tected from Insect visits and other agencies for the carriage 

 of pollen. For this purpose the best method Is to enclose 

 the entire Inflorescence (or in some instances the single 

 flowers) in bags of paraffin paper. These are made in 

 various sizes to order by A. G. Stursberg, New York City. 

 I have found the most generally useful sizes to be : 8 in. long 

 X3 in. wide, 10x4, 10x7^, 15x4, 17^x6, 19^4x153/^, and 

 20x9^. These may be attached to the plants in various 

 ways. I have used ordinary white cotton pack-thread, and 

 raffia, but have found the nurseryman's 33/<-Inch wired tree 



