4o8 Journal of AgricuHiire. [8 July, 1908. 



dwarfs, that is they produced tall and dwarf offspring in the ratio of 

 three to one, as in ttte case of the second generation of the original cross. 

 The results may be summarized as follows for three generations : — ■ 



Parents— Tall X Dwarf 



I 

 1st Generation — Tall (hybrid) 



I 



2inl (Jeneratioii— Tall (pure) 'ial Tall Dwarf (pine) 



I I I I I I I I ! I 



-3rd Generation -^Tall (pure) Tall Tall Tall Dwarf Tall Tall Tall Dwarf Dwarf (pure) 



(Ratio, 3 Tails to 1 Dwarf, and 1 pare Tall to 2 impure Tails.) 



The jKirents were a pure tall, fertilized by the pollen of a pure dwarf, 

 hut it did not matter as to the result which was the pollen-producing and 

 which the seedd^earing parent. For subsequent generations the pure tails 

 and the pure dwarfs alwavs bred true, and the hybrid tails always gave 

 tall and dwarf in the proportion of three to one, while of the tails, one 

 was Dure and two impure. 



Unit Characters. 



From the general results of his experiments, Mendel was led to the 

 idea of pairs of unit-cliaracters and that each germ-cell can carry one of 

 ;such a pair bu'l not both. He conceived the idea that the germ-cells of 

 the male (or pollen-cells) and female (or egg-cells) in a hybrid plant, each 

 ■contained one or other member only of any pair of unit characters 

 and that each member or factor of such a pair of characters is represented 

 in an equal number of germ cells of both sexes. Further, separate pairs 

 of unit-characters obey the law independently. Thus the germ-cell in the 

 hybrid pea represents either a tall or a dwarf but not both, and half of 

 them represent the tall and half the dwarf character. In the pure-breeding 

 tall pea, the geirm-cells only represerited the tall factor and those of the 

 dwarf onlv represented the dwarf factor. Now if we consider the result 

 or the union of sav 20 male germ-cells with a similar number of female 

 germ-cells, 10 of the 20 male germ-cells would be "tall" and 10 "dwarf " 

 and the same with the female germ-cells. As half of the germ cells are 

 " tall " and half " dwarf," there is an equal chance of 5 of the " tall " 

 male cells meeting and mating with 5 of the " tall " female cells, and 

 the same with regard to the dwarfs. So that the final result w'auld be : — 



:; Trill meeting Tall 



^ Tall meeting Dwarf 



S Dwarf meeting Tall 



i; Dwarf meeting Dwarf 



or a total of 15 Pure Tails, 10 Hybrid Tails and 5 Pure Dwarfs. 



It is generally assumed in breeding that hybrids show characters inter- 

 Tuediate between those of the parents, but carefully conducted experiments 

 prove that this is only one of many possibilities. If a red-fiowered pea, 

 for instance, is cros.sed with a white-flowered pea, the hybrid is not a 

 light-red but red like one of the pn rents. Red is doiiiiiiani o\er white and 



