HERBACEOUS AND WOODY DICOTYLEDONS 401 



Commercial varieties. The commercial varieties of the Cru- 

 ciferae are of the greatest importance economically and are also 

 of special interest to the student of variation and development 

 in cultivated plants, since some very remarkable transformations 

 have been effected in them by culture. Thus, in the cabbage 

 the stem has become greatly shortened and the normal leaves 

 transformed into the overlapping, fleshy leaves of the cabbage 

 head. In Brussels sprouts the stem has retained its normal length, 



Courtesy of American Magazine of .ForesfryTWashington, D.C. 



FIG. 252. Habit of violets with flowers 

 Photograph by Dr. R. W. Shufeldt 



but the lateral buds have been enlarged until they look like 

 small cabbage heads. In turnips and radishes the main tap- 

 root has become highly modified into the fleshy roots of the 

 commercial varieties. In the transformation of the cabbages, 

 cauliflower, Brussels sprouts, etc. mutation is thought to have 

 occurred, thus giving rise to some of the striking variations in 

 these plants which have been accentuated by- cultivation. 



VIOL ACE AE ( VIOLET FAMILY) 



The Violaceae are of special interest on -account of their 

 great beauty, both in the wild state and under cultivation. The 

 cultivated pansy is a hybrid of several wild species of violets. 



