136 ORIGINAL ARTICLES. 



casionally even necessary in plants apparently hermaphrodite. In other 

 species, cross-breeding between individuals or races is rare and excep- 

 tional, and apt to be unfruitful.* 



Plants of distinct species breed together only under exceptional cir- 

 cumstances. 



The hybrids thus produced are constitutionally more or less imper- 

 fect. They seldom produce a second generation, unless fertilized by an 

 individual of one of the parent species, to which they then gradually re- 

 turn. They, therefore, do not establish permanent races, but disappear 

 in nature, unless reproduced by a fresh cross-breeding between the pa- 

 rent species. 



Setting aside, in the first instance, these hybrids, and accidentally 

 abnormal extreme variations, monstrosities, and diseases, the variations 

 of a species may be generally referred to two classes. 



1. Variations resulting from the direct influence of soil, climate, 

 food, or other external circumstances, such as luxuriance from a rich 

 soil, fleshiness from a maritime exposure, &c. These act upon the in- 

 dividual ; they may disappear in that individual when the exciting 

 causes are removed, or they may become so engrafted on the constitu- 

 tion as to last through life, after removal of the causes ; they may even 

 become more or less hereditary through one or more generations. Seeds 

 of a plethoric kitchen-garden vegetable, originally the result of a pecu- 

 liar treatment in a rich soil, will, even under a different and uncongenial 

 treatment, to a certain degree reproduce the same variety for some gene- 

 rations. 



2. Variations which, arising from causes unknown to us, we consi- 

 der as constitutional, — variations in the colour of the flower, in the 

 form of particular parts, in the production or non-production of wings 

 or other appendages to fruits, seeds, peduncles, &c. These, like varia- 

 tions in the features of animals, are often hereditary, and in plants un- 

 der cultivation will last, or may be made (by selection of seed, &c.) to 

 last almost indefinitely ; and, in a wild state, they may, in particular 

 localities, result in apparently permanent races. These races, however, 

 generally breed readily with the typical forms of the species, and, al- 

 though permanent and distinct in some localities, will generally, in 

 some part of the area of the species, or under certain circumstances, be 



* Since the above was written out, and when on the point of reading it to the Society, 

 I observed in the "Gardener's Chronicle" of the 13th Nov., 1858, a very important com- 

 munication from Mr. Darwin, in which he states his conviction that this cross-breeding 

 between different individuals of the same species is universal. I admit readily that the 

 vast number of curious observations he has made, most of them hitherto unpublished, 

 tend to show that this cross-breeding is very much more general than we had supposed, 

 and perhaps indispensable in certain species, or, at any rate, under certain climatologi- 

 cal conditions ; but I think there are numerous facts which argue strongly against its 

 universality. On the other hand, Naudin, in a still more recent number of the " Annales 

 des Sciences Naturelles," in which he gives an account of some highly instructive expe- 

 riments connected with hybridity, may have been led too far in his doubts as to the fre- 

 quency of cross-fecundation in some of the genera he has experimented upon. 



