112 GOOD FROM CROSSING. Chap. XYLL 



their enormous roots. 63 have been transmitted to their progeny. 

 The result in all cases is probably in part due to the saving of 

 nutriment and vital force through the sexual organs acting imper- 

 fectly or not at all, but more especially to the general law of good 

 being derived from a cross. For it deserves especial attention that 

 mongrel animals and plants, which are so far from being sterile that 

 their fertility is often actually augmented, have, as previously 

 shown, their size, hardiness, and constitutional vigour generally 

 increased. It is not a little remarkable that an accession of vigour 

 and size should thus arise under the opposite contingencies of 

 increased and diminished fertility. 



It is a perfectly well ascertained fact 64 that hybrids invariably 

 breed with either pure parent, and not rarely with a distinct species, 

 more readily than with one another. Herbert is inclined to explain 

 even this fact by the advantage derived from a cross ; but Gartner 

 more justly accounts for it by the pollen of the hybrid, and 

 probably its ovules, being in some degree vitiated, whereas the 

 pollen and ovules of both pure parents and of any third species are 

 sound. Nevertheless, there are some well-ascertained and re- 

 markable facts, which, as we shall presently sue, show that a cross 

 by itself undoubtedly tends to increase or re-establish the fertility 

 of hybrids. 



The same law, namely, that the crossed offspring both of varieties 

 and species are larger than the parent-forms, hoi Is good in the 

 iio^t striking manner with hybrid animals as well as with mongrels. 

 rtlett, who has had such large experience says, " Among all 

 " hybrids of vertebrated animals there is a marked increase of size. 5 ' 

 He then enumerates many cases with mammals, including nionksys, 

 and with various families of bh 



On certain Hermaphrodite Plants which, either normally or abiior* 

 mall to be f> rtilised by pollen from a distinct individual 



or i 



The w to be given differ from the foregoing, as 



self-sterility is not here the result of long-continued close 

 interbreeding. Th< se facts are. however, connected with our 

 .: subject, 1 ecause a cross with a distinct individual is 

 shown to be eithei ry or advantageous. Dimorphic 



and trimorphic plants, though they are hermaphrodites, must 

 be reciprocally crossed, one set of forms by the other, in order 

 to be fully fertile, and in sonn - 8 to be fertile in any degree. 



63 k ..:"". 



63 Quoted by Dr. Marie, in ' Proc 

 61 Gartner, ' B&starderzeugung,' s, .... - 18' , j 40. 



