STERILITY 189 



enclosing the tassels do not unfold properly and the tas- 

 sel does not develop as it should. ' This is a secondary- 

 effect, but, nevertheless, is one factor in reducing fertil- 

 ity. The anthers are frequently much shrunken, some- 

 times shedding no poUen at all and even under the best 

 conditions producing a very meagre supply. The amount 

 of pollen produced is more affected by weather conditions 

 in such inbred strains than in more vigorous plants. At 

 the same time inbred strains of maize have been obtained 

 which show no degeneration in the staminate parts. Their 

 anthers are full and produce abundant pollen. Such 

 strains thus far have been few in number. They are cor- 

 related with poor development of the pistillate parts. 

 Those strains which have the best developed ears as a 

 rule have very much reduced tassels with a large amount 

 of pollen abortive. Some strains have been obtained which 

 are about equally well developed in both staminate and 

 pistillate functions, and these range all the way from 

 plants which are fairly productive for inbred strains down 

 to types which barely produce enough seed to survive, and 

 since many cases of failure to produce seed are met there 

 can hardly be a doubt that in some of them a complete 

 abortion of one or both functions has taken place. As in 

 the many other effects of inbreeding different results are 

 produced in different lines, showing clearly that segrega- 

 tion of certain factors influencing fertility has taken place. 

 On the whole, there is in this species a tendency for in- 

 breeding to result in a change from a monoecious condi- 

 tion to a functionally dioecious condition. 



Sterility in the form of structural degeneration when 

 it occurs gradually increases upon inbreeding until homo- 

 zygosity is attained, but for the most part it does not show 



