RESULTS OF SELECTION WITH SELF-FERTILIZED CROPS 123 



studied. The parental forms were grown with the hybrids for 

 comparison. Although tobacco is naturally self-fertilized, the 

 plants were bagged to insure self-fertilization. The behavior 

 of the parental forms selected in a plus direction is shown. It is 

 obvious from the data presented that tobacco, like other self- 

 fertilized crops, does not respond to selection within a pure line; 

 at least not to a degree which would encourage the plant breeder 

 to use this method of seeking improvement. (See Table XXII.) 

 Love and Craig (1918b) recently reported on the effect of 

 selection for height of plant within a pure line of oats. No evi- 

 dence of selective effect was obtained, as is shown in Table XXIII. 



TABLE XXIII. SELECTION FOR HEIGHT WITHIN A PURE LINE OF OATS 



Average height of parents 



Average height of offspring 



An average difference of 25.7 cm. in height of plant between 

 the parent forms chosen, failed to change the genotype. 



One of the old mooted questions among investigators of field 

 crops was the relation between the weight of seed planted and the 

 resultant yield. Earlier workers adhered to the belief that the 

 selection of large seed would give increased yield. In a pure line 

 of a self-fertilized crop, heavier seeds possess larger endosperms 

 a'nd consequently contain more stored food material for the young 

 plantlet than the smaller seeds. It seems that it would be pos- 

 sible to have the environment during the germination period 

 such that the larger seeds would have an advantage over the 

 smaller ones. The important fact to bear in mind, however, is 

 that all seeds of the same pure line have the same inheritance. 



Some work has been done (Arny and Garber, 1918) on the 

 relation between size of seed planted and resultant yield in 

 Marquis wheat. The seeds were individually spaced 4 in. apart. 

 The relation between the weight of the seed in milligrams, and 

 the resultant yield in decigrams was expressed by means of a 



