BOOTS 



these fruits may produce adventitious roots but they arise most 

 readily from nodes. Usually there must be favorable circum- 

 stances, such as burial in soil, a certain supply of moisture, and 

 darkness to promote growth of adventitious roots. In stems 

 which lie on the ground, as the runners of strawberries, roots 

 originate only at the nodes, 



12. Sports or mutations from root-cuttings. — Blackberries 

 are commonly propagated from root-cuttings and most varieties 

 come true ; some sorts, however, do not, the 



most commonly reported cases being Erie, 

 Eldorado, Wilson Junior, and Rathbun. 

 This phenomenon of root-cuttings that pro- 

 duce individuals different from those that 

 come from stem-cuttings has been found in 

 several other plants; as bouvardias, pelar- 

 goniums, and many variegated sorts, espe- 

 cially those with roots having a white core 

 and a green covering. Long unexplained, 

 this phenomenon is now called a periclinal 

 chimaera, a plant having a core of one va- 

 riety and a covering or cortex of another. 

 Adventitious buds on true roots are borne 

 from the plerome or core of the root, w^hile 

 those of the stem arise from parts of the 

 plant external to the plerome. Adventitious 

 buds on the roots are said to have an endogenous origin ; those on 

 branches, except those of monocots, an exogenous origin. Core 

 and covering in the blackberries that do not come true from root- 

 cuttings, and in the other plants named, according to this theory, 

 are of two varieties. 



13. The use of roots in classification. — Neither botanist nor 

 pomologist make much use of roots in classifying groups except 

 in grapes. In this fruit the structure of the root may be of 

 importance in distinguishing species. Thus, the roots of one 

 species, Yitis vinifera, are soft and succulent ; in all American 

 species, they are hard and fibrous. The root system of the 

 Labrusca grapes is shallow; that of Rupestris penetrates the 

 ground very deeply and has few lateral branches. One may tell 

 most species of grapes by a glance at the roots, and the grower 



Fig. 2. A grape 

 cutting with ad- 

 ventitious roots. 



