1912] Goodspecd: Xicofiaua Hyhrids 127 



2. Cross Pollination 



In preparing flowers for cross fertilization a number of pre- 

 cautions and as exact a routine as the circumstances permit 

 are rigidly enforced and any slip that can be detected serves to 

 put a stop immediately to the work in hand. It can be fairly 

 stated that the technique and methods developed in connection 

 with all matter pertaining to the iVi'co^iana-experiments have 

 reached a degree of refinement which cannot reasonably be sur- 

 passed without introducing minutiae of detail too complicated 

 to be practicable. The small size and great number of seed 

 borne by a Nicotiana plant introduce one of the greatest sources 

 of error in these experiments and has led to unusual precautions, 

 especially in the matter of cleaning, sowing and germinating 

 the seed. 



In the field the first precaution taken is one which undoubt- 

 edly is universally observed in such work (Shull, 1908a). The 

 arms are bared to the elbows and arms and hands are sterilized 

 in 95 per cent alcohol. A curve-pointed forceps and a small 

 pair of scissors are kept immersed in 95 per cent alcohol when 

 not immediately in use. Until the conclusion of the particular 

 operation under way the hands touch only the instruments and 

 the flower or flowers that are being worked with, and any contact 

 between them and the clothing or other plants nearby necessitates 

 at once a new sterilization. When an assistant is at hand it is 

 entirely possible in making, for example, a cross-pollination, for 

 the operator himself to do nothing more than pick out with the 

 forceps a stamen from one flower which has been brought to 

 him in its bag and apply the pollen-covered anther to the stigma 

 of the female parent. 



The male parent is prepared just as described above in con- 

 nection with the obtaining of pure seed. The label is given the 



plant number with the male sign writen directly after it — e.g., 



53 



03 J*. In work on .V. acuminata four or five sets of buds were 



prepared on a male parent at about the same time in order that 



there might bo no doubt of a sufficient supply of pollen in case 



of any errors in the sul)sequent operations. 



