INHERITANCE— IMPROVEMENT RY BREEDING 



53 



The tassels may appear before the silks, and sometimes even CHAP, 

 shed all their pollen before any silk appears (II 79). v - 



The appearance of the tassels is by no means uniform in 

 individuals of the same variety. This is an important point in 

 connection with the work of detasselling, for it makes it neces- 

 sary to go through the breeding plot three or four times, at 

 different dates, to effectually prevent self-pollination. 



189. Covering the Silks. — This is done by means of paper 

 bags similar to those used for covering the tassel (IT 188). The 

 ear should be covered just before the silks first appear, to pre- 

 vent contamination with stray pollen. The ear may be left 

 for four days or a week before the pollen is applied, in order 

 to ailow all the silks to develop. For pollination, the bag is 

 removed and a good dose of pollen shaken on to the silk, care 

 being taken that it reaches all the silks. The bag is then re- 

 placed quickly to avoid contamination with stray pollen. The 

 first attempts at hand-pollination are not always satisfactory, 

 but excellent ears may be obtained as a result of skill gained 

 by experience and practice. 



The silks may appear either before or after the tassels. 

 Not all the silks mature at the same time ; those from the 

 ovules lowest on the cob appear first. Sometimes fresh silks 

 continue to appear over a period of seven days. A single 

 hand-pollination, effected when the silks first appear, is therefore 

 inadequate ; nor is it sufficient to repeat it on two successive 

 days ; this results in the lower half of the cob being well-filled 

 while the apex remains undeveloped. Three pollinations, at 

 intervals of three days between each, generally prove the most 

 effectual, but by this means greater risk of contamination is 

 incurred. 



In some cases, and in the same breed, the silks appear be- 

 fore the tassels. When such an individual happens to be the 

 earliest to flower in a field, it may fail to develop seed ; this 

 tendency is therefore unlikely to be propagated to any great 

 extent. 



190. The F l Plants. — Three or four hundred grains will be 

 obtained from a single successful crossing. If the parents 

 differ in colour of endosperm, it will sometimes be possible to 

 tell which grains have been crossed and which selfed acciden- 

 tally, and the latter can be discarded. But F 1 seed should be 



