PLANT CHIMERAS 



Recent Spectacular Productions of Experimental Horticulture — Their Existence 



Known for Nearly Three Centuries — Only One of Them a 



True Graft Hybrid. 



The Editor 



TWO plants of different species 

 grown together so closely that 

 one forms the whole outside 

 like a glove and the other the 

 inside like one's hand; or like Siamese 

 twins, one species forming one side of 

 every part of the plant and the other 

 species the other side: such are plant 

 chimeras, perhaps the most spectacular 

 horticultural discoveries of recent years. 



Not that such things were never 

 known before. They were first reported 

 nearly three centuries ago, and doubt- 

 less existed centuries earlier, but un- 

 noticed. It was not until lately, how- 

 ever, that their production under ex- 

 perimental conditions, and the study of 

 their cells under the microscope, made 

 it possible for botanists to understand 

 exactly what they were. Now that we 

 know the trick, they can be produced 

 by anyone with patience, and the 

 mystery surroimding the so-called "graft 

 hybrid," a bone of contention among 

 horticulturists for several centuries, 

 has vanished. 



Broadly speaking, any plant produced 

 by grafting one species on another is a 

 graft hybrid. Such an operation has 

 been practised since prehistoric times, 

 and at present some plants are almost 

 never grown on their own roots, as the 

 saying is, but are grafted on some 

 hardier stock. Thus the Washington 

 Navel orange in California is regularly 

 grown on some such stock as the 

 pomelo, or the hardy and vigorous Citrus 

 trifoliata of Japan; and the resulting 

 trees are, in the broadest sense of the 

 phrase, graft hybrids, being the union 

 of two distinct species through grafting. 



But under these conditions, each of 

 the parent species maintains its separate 

 life, as far as the cells are concerned. 



These only come in contact along the 

 line where the graft was made ; the roots 

 remain just what they were — Citrus 

 trifoliata, in the case chosen for illustra- 

 tion; the branches remain just what 

 they were — Citrus aurantium, the navel 

 orange. Each species exercises a slight 

 influence on the one to which it is 

 united, but in general they maintain 

 their separate identity and their sys- 

 tems of cells come in contact, as was 

 said, only at one plane in the whole 

 plant. 



We can go two steps farther in the 

 production of graft hybrids, however. 

 First, we can produce hybrids where 

 the cell systems of the two parents are 

 in contact throughout much or most of 

 the plant; second, it appears that we 

 can produce hybrids where the cells of 

 the two parents actually blend. I shall 

 leave the latter case for discussion 

 further on, and explain in more detail 

 the commoner cases where the two par- 

 ents bear the relation to each other, in 

 the hybrid, of Siamese twins, or glove 

 to the hand it encases. A short account 

 of the way in which the nature of these 

 chimeras was discovered will perhaps be 

 helpful. 



HISTORY OF CHIMERAS. 



The first one brought to the attention 

 of men of science was a product of the 

 genus Citrus, and has always been 

 known as the Bizarria — because of its 

 bizarre appearance, of course. It now 

 exists in many forms, and new ones are 

 appearing almost every year. One of 

 the original type is shown in fig. 1 and 

 a recent specimen which sprang into 

 existence in Florida a few years ago is 

 shown in fig. 3. The original Bizarria 

 is said to have appeared in Florence, 



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