144 INBREEDING AND OUTBREEDING 



Kolreuter (125) has already remarked; when grown in pots and thus 

 limited in food supply their tendency is toward fruit development and 

 seed production. 



Besides possessing general vegetative vigor, hybrids are often 

 noticeable for the extraordinary length of their stems. In various 

 hybrids of the genus Verbascum, for example lychnitis-thapsus, the stem 

 shoots up 12 to 15 feet high, with a panicle 7 to 9 feet, the six highest 

 side branches 2 to 3 feet, and the stem 1 1/4 inches in diameter at the 

 base: in Althaea cannahino-officinalis the stem is 10 to 12 feet; in 

 Malva mauritano-sylvestris 9 to 11 feet; in Digitalis purpureo-ochroleuca 

 8 to 10 feet, with^anicles 4 to 5 feet; and in Petunia nyctaginifloro- 

 phoenicea and Lobelia cardinali-syphilitica 3 to 4 feet each. Prof. 

 Wiegmann also corroborates these observations. 



The root system and the power of germination of hybrids are 

 highly correlated with their great vegetative vigor. Many hybrids, there- 

 fore, which are not so luxuriant in growth as those just described, for 

 example Dianthus, Lavatera, Lycimn, Lychnis, Lobelia, Geum, and 

 Pentstemon hybrids, put forth stalks easily and therefore are readily 

 propagated by layers, stolons, or cuttings. The observa4;ions of Kolreuter 

 (125), and of Sageret (191) agree with ours in this respect. 



Luxuriation expresses itself at times as proliferation; for instance, 

 in Lychnis diurno-ftos cuculi the receptaculum is changed to a bud that 

 puts forth branches and leaves. If, moreover,, the vigor of the hybrids 

 especially affects the stem and the branches, particularly their length, 

 nevertheless the leaves take part in it by becoming larger. Hybrids in 

 the genera Datura, Nicotiana, Tropaeolum, Verbascum, and Pentstemon 

 are examples. 



Naudin,^^^ the contemporary of Mendel, whose ideas 

 very nearly resembled modern conception of heredity, 

 likewise gives many excellent illustrations of hybrid vigor 

 from interspecific crosses which he made in Papaver, Mir- 

 abilis, Primula, Datura, Nicotiana, Petunia, Digitalis, 

 Linaria, Luffa, Coccinea and Cucumis. Out of 35 crosses 

 within these genera 24 show positive evidence of heter- 

 osis. The cross of Datura Stramonium with D, Tatula 

 was particularly notable in this respect. Both reciprocal 

 hybrids were twice as tall as either parent. 



