PEDIGREE - CULTURE , - 



the pile of sterilized soil and from other seed-pans and after 

 the seeds are sown, a label is inserted, which bears the same 

 number as that on the seed-packet. Then the pan is set in a 

 shallow vessel of water until it is thoroughly subirrigated, 

 after which it is covered loosely with a clean glass plate and 

 removed to its final place in the propagating house. Only 

 one lot of seeds is handled at a time, and the hands are 

 thoroughly cleaned after completing the sowing of one lot of 

 seeds before opening the seed-bag or handling the pan which 

 is to receive the seeds of another pedigree. All watering 

 of seed-pans is preferably done from below, because the 

 slightest carelessness in throwing a jet of water on a seed- 

 pan might transfer a seed from one pan to an adjoining one. 

 If surface watering becomes at any time advisable, the indi- 

 vidual pans should be removed to a safe distance from all 

 others during the operation. In the case of surface-watering 

 it is also necessary to take thought as to the source of water 

 used. If from a protected well, it is all right, but at the 

 Station for Experimental Evolution the propagating house 

 is supplied from a reservoir which receives water from an 

 open stream, and there is no safety in using this water on 

 the seed-pans unless it is first filtered, because many small 

 seeds find their way into the reservoir and might be easily 

 conveyed into the seed-pans by surface watering. 



All of the foregoing matters are controlled with com- 

 parative ease, but there are sources of error which are much 

 more difficult to manage. The director of the experiments 

 understands the necessary precautions and takes them, and 

 so do his foreman and others regularly engaged about the 

 cultures, but not so the casual visitor. The plumber comes 

 in to repair a pipe. He does not take kindly to a request 

 that he brush the hayseed from his clothing before he enters 

 the propagating house. He is sure they will not shake off 

 while he is at work. Visitors want to see the cultures, and 

 it is disconcerting to them to be asked to keep their fingers 

 out of the seed-pans. I have often wondered what about a 



