



LOTSY, CURRENT THEORIES OF EVOLUTION. 407 
duce themselves mainly by broken off branches, in other 
words asexually, it is evident that it was this asexual mode of 
reproduction which preserved the diversity which was the result 
of crossing. I have no doubt that several of these forms will 
prove to be heterozygous and am looking forward to this being 
tested. 
The behaviour of plants, which have been multiplied in some 
asexual way, for a longer or shorter time, is of course a splendid 
test, as to their mode of origin. We all know, that when we sow 
the guarded seeds of tulips, hyacinths, plums, pears etc, and, as I 
have recently seen in Riverside, of Citrus also, we get a motley 
crowd, showing that all these domestic products are hybrids, and 
as there is every reason to believe — as DARWIN rightly insists 
upon — that new forms arise in nature in a similar way as under 
domestication, this fact again speaks in favor of hybridization being 
the cause of evolution. 
This origin by means of hybridization of our domestic plants 
may probably be extended to most of our domestic animals also. 
Mr. Houwiınk’s experiments in Meppel tend to show that at least 
three species of wild fowl, to wit Gallus bankiva, Sonnerati and 
furcatus have taken part in the formation of our domestic poultry, 
as he was able to show that hybrids between them are perfectly 
fertile, while Prof. GHia1 of Bologna has shown, that probably at 
least two species: to wit Columba livia and Columba leuconota 
have taken part in the formation of our domestic pigeons. 
That, also in nature, hybridization between animals is much more 
common than was suspected and that many so called species of 
wild animals are heterozygous, has been shown by GEROULD in the 
case of the alfalfa butterfly as well as in that of various other 
American insects and birds and by Gniıcı in the case of the 
pheasants of the Himalaya, in that of various species of birds 
around the Mediterranean and in that of African species of Numida. 
The Numida-case, the case of the guinea-fowl is especially inte- 
resting because DARWIN cites it as a case of an animal, which 
notwithstanding its transportation from an arid African habitat to 
-a humid English one, did not „vary”. 
GHIGI could prove that it does vary in the Darwinian sense in 
its native country, but only in those regions where it comes into 
