DIV. 11 PHYSIOLOGY 299 



The polarity which is noticeable in phenomena of regeneration also influences 

 the practice of grafting. Unlike poles of a plant may readily be induced to grow 

 together, while like poles may only be brought to do so with difficulty, and then 

 do not develop vigorously. 



The stock and graft influence one another in a variety of ways. 

 For example, portions of annual plants grafted on perennials attain an 

 extended period of life ; the opposite effect, a shortening of the life 

 of the graft, may also result from grafting. Qualitative changes may 

 also be brought about and may go so far as to lead to a vegetative bud 

 of the graft becoming transformed into a flowering shoot. The specific 

 properties of the two components are, however, maintained in cases of 

 transplantation. Certain cases known as chimaeras appear at first 

 sight to constitute an exception to this statement ; fuller investigation, 

 however, shows that while externally they appear intermediate forma- 

 tions between the symbionts in the graft, no mingling of the specific 

 characters has taken place. 



Chimaeras ( 61a ). Some plants grown in Botanic Gardens under 

 the names Laburnum Adami and Crataegomespilus suggest in a number 

 of ways comparison with hybrids (p. 317), but have undoubtedly not 

 arisen by sexual reproduction. Laburnum Adami (Fig. 264) is inter- 

 mediate between Laburnum vulgare and Cytisus purpureus ; it frequently 

 develops branches which can only be regarded as " reversions " to 

 Laburnum vulgare, and less commonly others that completely resemble 

 Cytisus purpureus. Certain intermediate forms between Crataegus 

 monogyna and Mespilus germanica are known as Crataegomespilus or 

 Bronveaux hybrids. The origin of these is known. The intermediate 

 forms, of which several are known differing from one another, arose in 

 the region of a graft of Mespilus on Crataegus in a garden at Bronveaux 

 near Metz. It can be regarded as certain that the origin of Laburnum 

 Adami was similar. Both plants have therefore been regarded as 

 graft hybrids, i.e. as hybrids not resulting from the union of sexual 

 cells, but by some influence of vegetative cells on one another. 



More recently HANS WINKLER has produced such " graft hybrids " 

 experimentally. He grafted Solanum nigrum, the Woody Nightshade, 

 on Solanum Lycopersicum, the Tomato, and after union had taken place 

 cut the stem of the stock transversely at the level of the graft. 

 Among the adventitious shoots which developed from the region of 

 junction of the two components there occurred well-marked inter- 

 mediate forms. In the first instance there were forms which were 

 composed of longitudinally-united halves with the characters of the 

 grafted plants ; these were termed chimaeras by WINKLER. Later 

 there were obtained other intermediate forms, externally uniform 

 (Fig. 265), which appeared to be the desired graft hybrids. Closer 

 investigation showed, however, that these also were to be regarded 

 as chimaeras, since they consisted of parts of the Tomato and the 

 Nightshade intimately united in growth but otherwise unchanged. 



