INHERITANCE—IMPROVEMENT BY BREEDING 231 



Cross-breds of unknown pedigree are difficult to deal with, CHAP, 

 and it may take years before they yield any desirable progeny. ' 



They should, therefore, be avoided, and the work of improve- 

 ment should be started with well-bred seed. 



Where it is desired to add new characters to a breed which 

 does not already possess them, cross-breeding must be resorted 

 to. The actual process of crossing is easy, but to isolate and 

 fix the desired type is an entirely different problem. Crossing 

 produces such varied heterozygous combinations that endless 

 confusion results, and it requires knowledge of the laws of in- 

 heritance, and infinite time and patience, to produce order 

 out of chaos. Therefore a'oss-breeding should only be practised 

 or permitted where the effect of crossing is understood, the object 

 sought is well known, and the method well planned. 



186. Reciprocal Crosses. — -Where it is desired to transmit 

 a definite unit-character from one breed to another, it appears 

 to be immaterial which breed furnishes the male and which 

 the female parent ; the results in the F., generation are usually 

 the same in either case. 



187. Method of Cross-pollinating. — -Cross-pollination is a 

 comparatively simple matter. The silks of the plant to be 

 pollinated must be carefully protected from the access of any 

 stray pollen (Fig. 90) ; and the pollen of the male plant must 

 be carefully collected so that it will not be mixed with stray 

 pollen of other plants in the neighbourhood. The pollen is 

 then shaken on to the silks and the latter are again covered 

 up until all danger from stray pollen is over. It should be 

 remembered that the pollen is light and easily carried by the 

 wind ; when the field or plot is in tassel, the air may be charged 

 with pollen grains, so that difficulty is experienced in pre- 

 venting contamination of the silks with stray pollen. 



1 88. Collecting the Pollen. — The tassel should be covered 

 with a paper bag, an ordinary 2 lbs. grocer's bag, of thin but 

 tough brown paper, is found satisfactory. This is tied tightly 

 round the stem below the lowest branches of the tassels. The 

 bag should not be placed on the tassels until the first anthers 

 appear on the terminal branch of the tassel, otherwise the 

 anthers are apt not to develop properly. In the Transvaal, 

 much of the pollen is found to lose its vitality after the third 

 day. 



