Oct. 8, 1921 Comparative Vigor of F^ Wheat Crosses and Their Parents 55 



termed "incrossed seed" and is used as a basis of comparison in deter- 

 mining the immediate effect of cross-pollination. The average weight of a 

 normally pollinated seed for all varieties used was 26.65 ±0.22 mgm./ 

 and the average for an incrossed seeds was 18.13 ±0.24 nigm. 



A comparison is shown in Table I of the hybrid seed and the incrossed 

 seed where the average dates of pollination are the same or approxi- 

 mately so. 



Table I.- 



-Weight of seed of the immediate crosses compared with weight of seed of the 

 incrossed parents 



a In the discussion of crosses the seed parent is given first. 



The varietal crosses in every case showed an increased seed weight as 

 compared with the female parent. The largest increase in seed weight 

 was 7.6 ±1.2 mgm., which was obtained from the cross Marquis X Penny. 

 This hybrid gave on the average over 50 per cent heavier seeds than 

 incrossed Marquis. Of the species crosses none gave a significant increase 

 in seed weight. Velvet Chaff crossed with Mindum produced seeds which 

 on the average were 4.0^0.8 mgm. lighter than the seeds of incrossed 

 Velvet Chaff. 



F, GENERATION CROSSES COMPARED WITH THEIR PARENTS 



Some of the earliest hybridization work affords good examples of the 

 vigor of Fi crosses. For an excellent review of this subject the reader is 

 referred to the publication of East and Jones {8) . 



In the present experiment the Fi generations and their parents were 

 grown in the greenhouse under controlled conditions. Care was taken 

 to plant seeds at a uniform depth, and when the seedlings were about 4 

 inches tall they were transplanted to 7-inch pots, two seedlings to a pot 

 and only like seedlings together. Unfortunately an epidemic of stem-rust 



1 The probable error of an average of averages was calculated according to the formula: 



in which n is the number of individuals in a generation, e the probable error, and A" the total niunbcr of 

 individuals (is). 



