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 laciniated beech gave only 10^ 

 of laciniated 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 



