47 



continuous series from the lowest to the highest. We have no 

 particular right to suppose that all plants can be traced back to 

 a single ancestor ; indeed, the evidence is against it. There is no 

 reason why several phyla, or lines of ascent, may not have orig- 

 inated, perhaps simultaneously, from the most primitive form of 

 living protoplasm. The story of the lower aquatic forms cer- 

 tainly indicates this possibility. Of these lower phyla some 

 stopped short, some went on, which ones is a matter to be defi- 

 nitely settled. A good instance, though a somewhat special one, 

 to illustrate the fallacy of the assumption of a single line of rela- 

 tionship, is found among the fungi, the chlorophylless lower 

 forms. Many ingenious authors have attempted to unite them in 

 a single continuous series, when every evidence we now have 

 points to their having originated at several places from the green 

 plants. Who, indeed, would care to deny that new phyla might 

 be originating to-day ? Any concept of evolution demands such 

 a possibility ; organisms are more plastic than the average person 

 conceives, even in this age. 



The object of a natural classification is to consider all the 

 many plant forms, to determine by such marks of genetic rela- 

 tionship as we can discover their place in the series, where they 

 have departed from the main stem and in how far they may have 

 had a line of development of their own. Despite what I have 

 said about the lower phyla, it is not improbable that the higher 

 plants can be traced back to some single source, not that it is to 

 be believed for a moment that this ancestor exists to-day. Liv- 

 ing ferns or mosses are no more to be considered the direct 

 ancestors of the flowering plants than are monkeys to be con- 

 sidered the direct ancestors of man. 



The establishment of our classification to-day might be com- 

 pared to the putting together of a puzzle map some parts of 

 which are lost ; we can determine how many of the parts fit 

 together, and, by analogy, can tell something of the missing 

 ones. The whole method depends on the admission of genetic 

 relationship, a concept that is built up partly by the study of 

 adult structure, partly by the story of the developmental stages, 

 partly, though m botany less than in zoology, by the evidence 



