SYSTEMATIC BOTANY 87 



the plant known as Ginkgo Uloba has no fellow-species 

 in its genus, but is a single species composing a genus, 

 and that genus by itself composes a family, and there 

 are good grounds for putting that family in a phylum 

 by itself. Thus, one single species by itself can form a 

 whole phylum of plants, while in other cases there 

 may be a thousand species or more in a phylum. In 

 such a case that single species is obviously of greater 

 interest and importance than one of the thousand. In 

 the case of the Ginkgo just mentioned the reproductive 

 organs have some unusual features, of which the most 

 striking are the motile sperms, which swim like in- 

 fusoria in a drop of water and are found in none of the 

 higher families of plants but Ginkgo and the Cycads, 

 and are similar to those in the ferns. The genus is 

 interesting also in being the only representative left 

 alive of a once large and widespread group. To the 

 philosophical systematist, therefore, all his species are 

 not of the same value, but all must be registered with 

 equal care. The correct registering of the known plants 

 of the world is the first duty of systematists a know- 

 ledge of their inter-relations and phylogeny the greatest 

 result of their work. 



