56 



THE PLANT WORLD 



the autoclav needs no other solution. As the Station for 

 Experimental Evolution has no gas, resort was had to an 

 alcohol blast-lamp. At first the autoclav radiated more heat 

 than the lamp could supply, before it reached an adequate 

 temperature, but this was remedied by jacketing the drum 

 with felt herbarium driers. 



If an autoclav is not available the soil might be freed 

 from seeds by boiling or baking but in both cases the mechan- 

 ical condition of the soil is apt to be greatly injured. My 

 experiments were begun without a sterilizer but instead of 

 germinating the seeds in garden soil I used sand from a gla- 

 cial deposit taken in such manner as to avoid the possibility 

 of contamination with seeds which might have been carried to 

 the surface of the sand by the wind or any other agency. The 

 desired result was attained in this way, as no foreign seed- 

 lings appeared, but at the expense of failure to get satisfac- 

 tory germination in many species for whose early develop- 

 ment the mechanical qualities of sand are apparently un- 

 suited. 



The care and handling of the sterilized soil present 

 many problems. No permanent supply can be safely kept and 

 all soils should be sterilized from day to day as they are 

 needed. Those who handle the soil must keep their clothing 

 brushed and their hands and nails clean. The soil-bench is 

 carefully swept and covered with clean newspapers before the 

 soil is turned out of the vessels in which it has been sterilized. 

 The sifters and other implements used in handling the steril- 

 ized soil, if of a character which makes their perfect cleans- 

 ing difficult, must never be used for unsterilized soil. I use 

 only square earthen seed-pans 30 cm. at the top, 25 cm. at 

 bottom and 7 cm. deep. These are thoroughly scrubbed 

 before using. Wooden boxes of similar dimensions were 

 used at first, but the difficulty of freeing them from seeds 

 which might remain in the joints led me to discard them 

 after once using. After the seed-pan has been made ready for 

 the sowing of the seeds, it is removed to a safe distance from 



