120 



The Journal of Ilercdily 







iP^A. 





I'artial I)efe<-tive Coniplcte Defective Both Types 



A CROSS BETWEEN TWO TYPES OF DEFECTIVE ENDOSPERM 



Figure 11. These ears are borne on plants of the first hybrid generation, but because 

 of the phenomenon of double fertilization in maize the endosperm of these grains is of second 

 generation tissue. Only one type of defective grains occurs on some ears, while on others 

 both types are found. On the ears on which both types occur they are in a 9:7 ratio, proving 

 that tine two defects are genetically distinct. 



Description cf Characteristic Types 



A tvjjical representatixe of the first 

 grou]) is one which Jones first oh- 

 served in a commonly thrown New 

 England variety. Century Dent. This 

 particular defective is little more than 

 an em]jt\' ])ericarp, although under 

 certain favorahle conditions, it does 

 form a trace of endos])C'rm tissue. The 

 .seeds have a very small embryo, scarce- 

 ly visible excei)t under the microscope, 

 but ap])arently quite normal in struc- 

 ture. When kept in a germinator at 



optimum conditions of temperature and 

 moistui'e, these aborted seeds show a 

 germination of about twelve per cent. 

 The seedlings are e.xtremely Weak, as 

 shown in the illustration, and in many 

 cases are unable even to burst through 

 the i)ericarp. Because of the almost 

 complete absence of an available food 

 sui^ply, these seedlings survive but a 

 few days. It has been possible to 

 ])rolong their period of development 

 by growing them in a nutrient agar, 

 and it might be possible by grafting 



