Practice of Plant Breeding 



brated botanist, De Vries, found a plant of clover in 

 which some of the leaves had four and five leaflets. By 

 selecting from these clover plants he obtained races in 

 which four and five leaflets were the usual character. 

 But some of the leaves had six and seven leaflets. It 

 is very unlikely that any clover plant in the world 

 ever had seven leaflets until De Vries started those 

 experiments. 



The second method, that of hybridising, has been also 

 found extremely useful in practice. 



Natural hybrids are common enough, and especially 

 amongst willows, brambles, and mints. (Long lists of 

 natural hybrids will be found in the ft Report of the 

 Conference on Genetics," published by the Royal Horti- 

 cultural Society in 1906.) 



But they do not seem able to survive under natural 

 conditions. Mentha sativa is said to be a cross between 

 M. arvensis and M. aquatica, but it cannot hold its own 

 in competition with its parent species. 10 



All sorts of experiments have been carried out in 

 hybridisation. 



One of the most unexpected has been the production 

 of odd and strange ferns. 11 The spores of many kinds 

 of ferns are all sown together on damp soil. So soon 

 as the prothallia are in good healthy development, the 

 place is flooded with tepid water for a few minutes. 

 Some of the antherozoids (male cells) succeed in reach- 

 ing the egg cell of some other kind of fern, and a weird 

 but valuable mongrel may be the result. 



In Florida a severe winter may destroy the ordinary 

 Mediterranean oranges, but by crossing the valuable 

 races with Citrus trifoliata, which is able to resist cold, 

 the citranges " Willits " and " Rusks " have been pro- 

 duced, and these are found to be of great value. 12 



Amongst other triumphs in this line of research are 



287 



