PEDIGREE - CULTURE 



55 



Lastly the specimens of the exsiccata it must be remem- 

 bered, lose with years of preservation, the intensity of their 

 color, due to the lack of moisture for the alga, until they 

 finally become of a pale and dirty yellowish, and their mor- 

 phology, alone, makes determination possible. 

 Concord, Mass. 



THE PEDIGREE-CULTURE: ITS AIMS AND 



METHODS. 



By Dr. George Harrison Shull. 



{Coftclusion.) 



The handling of the seeds is the next crisis in the pedi- 

 gree method. Each seed-bag is labelled at the time the seed 

 is collected, and to make doubly sure of the correctness of 

 the record the w^ooden label is taken from the seed-bearing 

 plant and enclosed with the seeds until a later date when 

 the pedigree records are being made. The wooden label is 

 then removed and carefully compared with the data on the 

 bag and in the record. 



As all garden soil contains numerous viable seeds it Is^ 

 necessary that the soil to be used in the germination of pedU 

 gree seeds, shall be freed from all other seeds. For this 

 purpose the autoclav sterilizer has proved very satisfactory. 

 This consists essentially of a steam-tight drum fitted with a 

 thermometer and steam gauge. An Inch of water Is poured 

 into this drum and the soil is put into it in suitable balled 

 receptacles made to fit the Interior of the sterilizer. When 

 the lid Is clamped on, heat Is applied to the bottom of the 

 drum until the steam pressure within is raIsedto5 — 15 pounds 

 to the sq. In. and this pressure Is sustained for about five 

 hours. If It were necessary this process might be repeated 

 the following day, but experience has shown that few If any 

 seeds can withstand the temperature of 110° C. for 5 hours 

 when in the somewhat moist state in which they are sure to 

 be in the soil. When gas Is available the problem of heating 



