560 THE GENESIS OF NEW FORMS AS A RESULT OF CROSSING. 



intermediate between their progenitors ; here again, however, forms are not always 

 alike, and sometimes several intermediate forms make their appearance. If the 

 hybrid derived from Cirsium Erisithahs and G. Pannonicum, which inherits equally 

 from both parents, be crossed with pollen from Cirsium, Erisithales, the resulting 

 individuals have a stronger resemblance to the latter species and are instances of 

 goneoclinic hybrids. But when Cirsium Erisithales and C. Pannonicum are 

 crossed for a first time hybrids are also produced which are not exactly midway 

 between the parents but are more like C. Erisithales. These naturally resemble 

 the goneoclinic hybrid derived from crossing the offspring of C. Erisithales and C. 

 Pannonicum with C. Erisithales, and if one were not in a position to follow the 

 history of the origin of the hybrid in question its characteristics alone would not 

 furnish sufficient data for a judgment as to the mode of production of the goneo- 

 clinic hybrid. 



Hybrids which are the offspring indirectly of three different species are called 

 ternary hybrids. The word "indirectly" must be specially emphasized here, lest 

 the reader should fall into the error of supposing it to be possible that pollen-tubes 

 from two or more species should simultaneously fertilize a single ovule. Such an 

 occurrence never happens, not even if a mixture of pollen belonging to two or more 

 difierent species be placed upon the stigma of a particular flower. On the other 

 hand, it has been ascertained by numerous experiments that if the hybrid-offspring 

 of two species is crossed with the pollen of a third species, or vice versa, another 

 hybrid is produced. Thus, for instance, if the hybrid of Linaria genistifolia and 

 L. purpurea is crossed with the pollen of L. striata the result is a ternary hybrid. 

 In one experiment the stigmas in a capitulum of Cirsium Linkianum (the hybrid 

 offspring of C. Erisithales and C Pannonicum) were dusted with pollen taken 

 from C. palustre. A considerable number of fruits ripened, and the hybrids which 

 arose from them were ternary hybrids, exhibiting marks and characteristics of 

 C. Erisithales, C. Pannonicum,, and C. palustre respectively. These hybrids, more- 

 over, were not all alike; some of them bore striking resemblance to Cirsium aquilo- 

 nare, the hybrid produced by crossing C. palustre and C. Pannonicum, and exhibited 

 very few of the peculiarities of C. Erisithales, whilst other individuals were ex- 

 tremely like Cirsium, ochroleucum, the hybrid obtained by crossing C. Erisithales 

 and G. palustre, and only showed slight indications of its relation to G. Pannoni- 

 cum. Growers of garden-flowers have achieved great success in producing orna- 

 mental ternary hybrids in a number of genera (Achimenes, Begonia, Dianthus, 

 Gladiolus, &c.). Ternary hybrids of various Willows are also met with in 

 gardens; one of these is obtained by crossing Salix Gremsensis, a hybrid of Salix 

 Gaprea and S. daphnoides, with S. viminalis, another by crossing Salix WichurcE 

 (the hybrid-product of S. incana and S. purpurea) with S. cinerea, and so forth. 

 Willows have been also used for the prosecution of still further experiments. The 

 crossing of two hybrids of different parentage on both sides resulted in the genesis of 

 hybrids combining four species of Willow. Indeed, six different species of Willow 

 have on one occasion been combined by successive crossing — Wichura having 



