MULING IS CONFINED WITHIN NARROW LIMITS. 497 



tnm self-impregnated, either naturally or artificially, they are com- 

 monly more fruitful than they were after the first impregnation. As 

 might he expected, the seedlings approach nearer to the paternal type : 

 when the original simple mules in their second generation and the 

 paternal hybrids of the second degree exhibit a return to the type of 

 the maternal ancestor, such a return is never perfect, but only partial. 



This power of muling, properly so called, is confined within 

 very narrow limits, and can hardly be said to exist at all 

 between species of different genera, unless under that name are 

 comprehended some of the spurious creations of inconsiderate 

 botanists. There are, indeed, many cases of species very 

 closely allied to each other which it is either impossible to 

 mule, or so difficult that no one has yet succeeded in effecting 

 it. Mr. Knight never could make the Morello breed with the 

 common Cherry. I have in vain endeavoured to mule the 

 Gooseberry and Currant, and we do not possess any garden 

 production known to have been produced between the Apple 

 and the Pear, or the Blackberry and the Easpberry, any of 

 which might have been expected to intermix. As to mules 

 obtained between plants of distinct genera, we have, no doubt, 

 upon record, some experiments said to have been performed 

 successfully in crossing a Thorn- Apple with Tobacco, the Pea 

 with the Bean, the Cabbage with the Horseradish, and so on ; 

 but Mr. Herbert regards these cases, and I think with great 

 reason, as apocryphal, and not to be relied on ; the fact being, 

 as he truly states, " that in this country, where the passion for 

 horticulture is great, and the attempts to produce hybrid inter- 

 mixtures have been very extensive during the last fifteen years, 

 not one truly bigeneric mule has been seen." 



He never could cross a Bomarea aniAlstrcemeria, near as they are to 

 each other. But he succeeded, without difficulty, in making Sermione 

 Ajax, and Queltia breed together, as might have been anticipated from 

 the unbotanioal grounds upon which these spurious genera have been 

 carved out of Nar^iiasus. The long and carefully conducted experi-. 

 ments of Geertner ended in the same result ; and this author remarks, 

 that supposed eases of muling between Cucumis and Melo, Cheiranthus 

 and Matthiola, Brassica and Buphanus, Lychnis and Saponaria, 

 Pisum and Vicia, and some others, all seem to be more or less uncertain 

 in some part of their history. 



