The Making of Species 



FERTILE CROSSES BETWEEN SPECIES OF PLANTS 



In the case of plants the number of fertile 

 hybrids between species is so large that we 

 cannot attempt to enumerate them. De Vries 

 cites several instances in Lecture IX of his 

 Species and Varieties : Their Origin by Mutation. 



One of these the hybrid between the purple 

 and the yellow species of Lucerne which is 

 known to botanists as Medicago media is, writes 

 De Vries, " cultivated in some parts of Germany 

 on a large scale, as it is more productive than 

 the ordinary lucerne." Other examples of per- 

 fectly fertile plant hybrids cited by De Vries 

 are the crosses between Anemone magellanica 

 and A. sylvestris, between Salix alba and Salix 

 pentandra, between Rhododendron hirsutum and 

 R. ferrugineum. 



He gives an instance of a hybrid sEgilops 

 speltaformis, which, though fertile, is not so 

 fertile as a normal species would be. It is worthy 

 of note that Burbank of California has obtained 

 a hybrid between the blackberry and the rasp- 

 berry, which is not only fertile, but quite popular 

 as producing a novel fruit. 



STERILE PLANT HYBRIDS 



De Vries does not cite nearly so many examples 

 of sterile hybrids, presumably because they are 

 not so easy to find. He mentions the sterile 



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