L922.] 



Thiai.s or Ni;\v Varieties or Ckui-.ai.s. 



349 



Character of Seed. — A necessary precaution which has often 

 been neglected in variety trials is to make sure that the parcels 

 of seed of the different races under comparison are equally repre- 

 sentative. Very considerable differences in yield arise from 

 differences in the physical, germinative, and other non-racial 

 characters of the parcels of seed sown. These should not be 

 neglected, just as for other reasons in a variety trial of potato 

 we should not think of comparing Scotch grown " Arran Chief " 

 with Fen grown " Up-to-date." 



The function of a seed, as of a tuber, is to give the individual 

 plant a start. Much depends on a good start, and varieties should 

 not be irregularly handicapped in this respect. 



The only practicable method of eliminating this probable source 

 of error is to use seed of all the races under trial which has 

 been grown and harvested the previous year under uniform con- 

 ditions, and in case there is any substantial difference in moisture 

 content it would be preferable that all the parcels of seed should 

 be kiln-dried to an equal moisture content. 



A very good parcel of seed of an inferior race of a cereal will 

 sometimes give a better crop than an inferior parcel of seed of 

 a better race, but there is no evidence that this accidental quality 

 of the seed would be transmitted to the next generation. 



Admixtures. — Another systematic error arises if any sub- 

 stantial admixture occurs in the seed of any race under trial. 

 A very small percentage of admixture may be regarded as 

 negligible. One per cent, of " rogues," if of an obviously 

 different race of the same species will show quite forcibly when 

 the crop is ripe, but if the " rogue " plants are only 10 per 

 cent, less or more prolific than the rest, the difference in yield 

 due to them will only amount to one-tenth of 1 per cent., which 

 is negligible. If, however, the crop is to be used for sr rwing 

 again, even such a percentage is very undesirable. 



Casual Sources of Errors. — These are very numerous. They 

 include soil variations due to a multitude of causes and extend- 

 ing over large or small areas, such as those due to previous 

 cropping and manuring, soil bacteria, etc.; variations in sub-soil 

 and in natural or artificial drainage; contour variations, such as 

 si pes or furrows; irregular shading or uneven exposure to wind ; 

 patches of weeds of all sizes - inroads of insects, vermin, birds, 

 :■!<-.. in patches. Tt is quite impossible to exclude these sources 

 of casual errors and they may occur in either small or large 

 patches. Their occurrence may be regarded as ch in- - vents 

 and they may be all Lumped together, bec&us i there is only one 



