THE INTERNATIONAL PLANT-BREEDING CONFERENCE. 469 



inexhaustible perseverance. Gartner especially, in his "Die Bas- 

 tarderzeugung im Pflanzenreiche" (The Production of Hybrids in 

 the Vegetable Kingdom), has recorded very valuable observations; 

 and quite recently Wichura published the results of some profound 

 investigations into the hybrids of the willow. That, so far, no 

 generally applicable law governing the formation and development 

 of hybrids has been successfully formulated can hardly be won- 

 dered at by any one who is acquainted with the extent of the task 

 and can appreciate the difficulties with which experiments of this 

 class have to contend. A final decision can only be arrived at when 

 we shall have before us the results of detailed experiments made 

 on plants belonging to the most diverse order. Those who survey 

 the work done in this department will arrive at the conviction that 

 among all the numerous experiments made not one has been car- 

 ried to such an extent and in such a way as to make it possible to 

 determine the number of Siiferent forms under which the offspring 

 of hybrids appear^ or to arrange these forms with certainty accord- 

 ing to their separate generations, or to definitely ascertain their 

 statistical relations." 



This was the first suggestion that plant-breeding was subject to 

 mathematical laws. 



Mendel's law may be stated briefly as follows : "In the second 

 and later generations of hybrids every possible combination of the 

 characteristics of the parents occurs, and each combination appears 

 in a definite proportion to the number of the individuals.'' The 

 essence of Mendel's discovery is that the germ cells of the parents 

 contain unit characters in pure form. When two plants, A and B, 

 of definite opposing characters, are crossed there is no means of 

 predicting the character of their progeny, which mav be expressed 

 by AB. ' ' . 



The word "gamete" should now be defined. Gamete means 

 an egg cell, either male or female. When the gametes A and B 

 combine in sexual union the result will be AB. According to the 

 law of chance one thousand gametes A combine with one thousand 

 gametes B in the following proportions: %,ov 250, AA ; /4.or 250, 

 AB; >4, or 250, BA; ^,or 250, BB. 



These are all the possible combinations of the gametes A and B. 

 It is found by experiment that the plants AB are in all respects 

 the same as BA. If these plants are close-fertilized it is found that 

 in the next generation the AA will produce AA, and the type will 

 be fixed at once. The same is true of the descendants of the BB 

 plants. The remaining fifty per cent will be found to split up in 

 the next generation, as before, into 25 per cent AA, 50 per cent 



