336 Plant Life and Evolution 



plants like the parent, but a sporophyte bearing many 

 asexual spores, so that, as in the green algae, a single 

 fertilization results in the production of many new 

 individuals. 



HYBRIDIZATION 



Natural Hybrids. It was long the general be- 

 lief that true hybrids were necessarily sterile, but 

 experiment has shown that hybrids may be quite as 

 fertile as the parent species, or even in some cases 

 may surpass them in fertility. This at once opens 

 up the question whether new species may not some- 

 times arise immediately as the result of crossing of 

 two other species, and there is abundant evidence 

 that this is sometimes the case. While hybrids are 

 usually of rare occurrence in nature, there are many 

 records of such, and in some cases they occur in 

 numbers equal to the parent species, and are appar- 

 ently quite as well fitted to survive. These natural 

 hybrids have been much more carefully studied in 

 Europe than in America, where the number of au- 

 thentic cases is relatively small. Kerner estimates 

 that about one thousand natural hybrids have been 

 found in Europe, but of these only a small number 

 have survived and perpetuated themselves. As these 

 latter may be perfectly fertile and apparently fitted 

 to their environment, it is hard to see why they 

 should not be considered as good species. Most of 

 these were described as valid species before their 



