170 Plants and their Ways in South Africa 



out so that half the spores convey paternal and half maternal 

 characters. 



If the characters are contrasting ones as short and tall, 

 smooth and hairy, one will be suppressed by or recessive to 

 the other and will not appear in the hybrid of the next genera- 

 tion but in the generation following unexpected combinations 

 may occur. 



If the characters are not contrasted so that one suppresses 

 the other, a blend of characters may occur. For example, if 

 two white sweet peas be crossed, one with long pollen and a 

 flat standard (back petal), the other with round pollen grains 

 and a hooded or incurved standard, all the flowers of the next 

 generation (F 1 ) will be of two shades of purple with flat standard 

 and long pollen. 



The characters determining the flat standard are said to be 

 dominant to the hooded characters and long pollen is domi- 

 nant to round. These characters separate out in the pollen 

 and ovule of this generation, and in recombining, produce in 

 the next generation (F 2 ) a great variety of colours, combined 

 with either long or round pollen and flat or hooded standards. 

 Look in your garden of sweet peas and see if the hooded 

 standard is found with all colours. 



The combinations will not be haphazard as may at first 

 appear ; the world is indebted to Mendel, 1 who experimented 

 in his convent garden fifty years ago, for showing that the com- 

 binations occur according to definite mathematical laws. It is 

 not known that all hybrids behave according to the Mendelian 

 law, but the clue which Mendel gave is being used to-day in 

 scientific plant breeding. 



The law in its simplest form for simple hybrids may be 

 expressed in the accompanying diagram. 



Let A and B represent two unit characters, A being 

 dominant to B. In the first generation A< in which 

 these two characters are crossed only A will appear. In 

 the spores of this generation the unit characters will separate 

 out, and in the next generation, fertilization may effect a 



1 Since Mendel experimented with his peas, de Vries Correns and 

 others have revived and greatly extended this work. 



