2o8 MAIZE 



CHAP, transmitted from them to the silks of plants which are to be 

 kept pure. In spite of all possible precautions, seeds of un- 

 known paternal ancestry do creep into the cultures. With 

 tassels bagged three days before any pollen was ripe, it was 

 found that stray pollen was already present, and though old, a 

 certain percentage was viable, although East and Hayes con- 

 clude that the possible error from this source would be only 

 one to about 10,000. But in the bagging of the silks there 

 is also a chance of enclosing foreign pollen ; the same investi- 

 gators have found that about one ear in five would have one or 

 more grains so crossed, even when the greatest care was taken. 

 They conclude that in this work there is a possibility 

 of an experimental error of five or six seeds out of the 

 200 to 800 produced on an ear ; this is to be considered 

 as a maximum and not the probable error, the latter being 

 less than one seed per ear. As they well observe, however, 

 " the determination of a probable error in a mass of data is 

 not sufficient in genetic work ; an actual error, in which a 

 single seed of unknown paternity becomes the ancestor of a 

 pedigreed line, is sufficient to upset all inductions drawn from 

 the data". 



(b) The small size of the chromosomes makes them diffi- 

 cult to study. 



(c) And, finally, maize seed is rather delicate ; when pro- 

 perly matured and dried it remains in fairly good condition for 

 only three seasons ; seed older than this is almost worthless, 

 and there is even a possibility of the results from second year 

 seed being distorted. 



All these factors add to the difficulty of carrying out in- 

 vestigations. 



Methods of Plant Breeding. 



A man should be very careful in the selection of his parents. 



— Heine. 



163. A Few General Principles. — In plant breeding it is 

 necessary to carefully decide upon an ideal and to work 

 steadily and persistently toward it. We must remember that 

 it takes several generations of the plant to acquire and fix a 

 desired character, and that any deviation from the original aim 



