196 Retrograde Varieties 



taining as much as 20^ of red-flowered speci- 

 mens. 



Many fine varieties are recorded to come true 

 from seed, as in the case of the holly with 

 yellow fruits, tested by Darwin. Others have 

 been found untrue to a relatively high degree, 

 as is notorious in the case of the purple beech. 

 Seeds of the laeiniated beech gave only 10^ 

 of laeiniated plants in experiments made by 

 Strasburger; seeds of the monophyllous aca- 

 cia, Rohinia Pseud-Acacia monophylla, were 

 found to be true in only 30^ of the seedlings. 

 Weeping ashes often revert to the upright type, 

 red May-thorns {Crataegus) sometimes revert 

 nearly entirely to the white species and the 

 yellow cornel berry is recorded to have reverted 

 in the same way to the red berries of the Cor- 

 nus Mas. 



Varieties have to be freed by selection from 

 all such impurities, since isolation is a means 

 which is quite impracticable under ordinary 

 circumstances. Isolation is a scientific require- 

 ment that should never be neglected in ex- 

 periments, indeed it may be said to be the first 

 and most important requisite for all exact re- 

 search in questions of variability and inherit- 

 ance. But in cultivating large fields of allied va- 

 rieties for commercial purposes, it is impossible 

 to grow them at such distances from each other 



