MODERN PLANT-BREEDING METHODS 705 



complete way. Writing soon after the rediscovery of these 

 laws, Bateson ventured to declare that Mendel's experiments 

 were worthy to rank with those which laid the foundations 

 of the atomic laws of chemistry, and now that many 

 workers have shown that they apply not solely to the plants 

 with which Mendel himself worked, but to all the plants 

 and animals with which experiments have now been carried 

 out, few who realise the importance of an exact knowledge of 

 heredity will be found to dispute the statement. 



With the knowledge that law and order underlie the pheno- 

 mena of hybridisation came the realisation that breeding must 

 soon depart from the haphazard methods of old, and in their 

 place careful studies of the inheritance of all the characteristics 

 in which the breeder was interested must be made in order to 

 obtain definite instead of chance results. The experiments to be 

 described now were planned with the object of testing Mendel's 

 laws and determining to what extent they would afford help in 

 solving the complex problems which the breeder has to face. 



They are concerned with most of the crops of the farm, but 

 at present the investigations on cereals only will be described. 

 These plants are particularly suitable for the study of such 

 problems on account of the fact that they are so invariably self- 

 pollinated that complications due to vicinism are not likely 

 to occur. The one drawback to their employment is the fact 

 that each crossing gives one grain only, and where the gametic 

 output of any plant has to be investigated the mere making of 

 sufficient crosses becomes a matter of some difficulty. 



The results have proved unusually simple, and certain of 

 them may be quoted here in order to give an explanation of 

 the main points in the Mendelian story and to show how its 

 principles may be employed for the improvement of our 

 cultivated plants. For this purpose the details of a cross 

 between two varieties of barley, Hordeum vulgare and H. Steudelii 

 happen to be particularly suitable. 



In Hordeum Steudelii the medium floret of the group of three 

 which is characteristic of all barleys is hermaphrodite, whilst the 

 two lateral florets are rudimentary and entirely devoid of sexual 

 organs. The ear is thus flat or two-rowed. Its awns and 

 paleae are a dead-black colour. In H. vulgare all three florets 

 of each group are hermaphrodite and fertile. The barley is 

 thus six-rowed : the paleae and awns are white in colour. 



