36 NINTH REPORT. 



jected various substances, radium preparations, sugar solutions, calcium 

 nitrate, and zinc sulphate, into the capsules of the plants experimented 

 upon, before the eggs were fertilized by the nuclei from the pollen grain. 

 From the many capsules used, a few furnished seeds which, on planting, 

 produced plants notably different from the type of the parent plant. The 

 flowers of the new type were closely guarded to prevent cross fertilization, 

 and their seeds when planted gave a few plants which conformed in every 

 particular to the new type. 



If there is no mistake about Mac Dougal's results, and I see no reason for 

 supposing there is, at least one very important conclusion seems to be well 

 founded, namely, that in an early stage of development of the plant egg, 

 before it has been fertilized, it may be so profoundly modified that the adult 

 plant resulting from it is decidedly different from what it would have been 

 had the egg not been so modified, and the modifications thus produced are 

 transmitted to the next generation through the seeds. Taking tlie results 

 of both de Vries and Mac Dougal, we may conclude that the necessary mod- 

 ification of the egg is sometimes produced in nature, and may also be induced 

 by means under the control of the experimenter. 



There is one c^uestion which will probal^ly be both affirmed and denied by 

 different biologists for some time in the future. It is this: Are the new 

 types which appear by sudden leaps to be considered new species or only 

 varieties of the jjarent species. The debate on this ciuestion will be all the 

 more acrid and prolonged because of the impossibility of giving a satisfac- 

 tory definition of the term species. 



One ought to ask pardon perhaps for ciuoting authority in science, but a 

 high botanical authority has said that he believes no better definition of 

 species has ever been invented than this: "A species is a perennial succession 

 of like individuals." An equally high botanical authority has said that a 

 species is a judgment. And this also is true. Species and other categories 

 of classification are more or less arbitrary distinctions, made for convenience 

 in classification of our knowledge. Hence in a given case, the question 

 whether two different forms are to be regarded as two different species or 

 not, is in part a matter of individual judgment. If Darwin's view is correct 

 that new species may originate by the gradual accumulation of exceedingly 

 minute differences, there could be no line of demarkation between species 

 provided we could have all the transitional forms. Only where the transi- 

 tional forms had disappeared, or the new forms had migrated to a new re- 

 gion, could we have sharp lines of distinction between species. Even in 

 the case where the new form had migrated to a region not occupied by the 

 old, the transitional forms would be disclosed on studying the species in all 

 its range. Distinctions of species in such a case must necessarily be more 

 or less a conventional matter. But if species originate by the sudden produc- 

 tion of entirely new characters, that is by mutations, as de Vries believes, 

 then there are no transitional forms connecting the new to the old. The 

 condition in nature in this case would be similar to that in which there has 

 been an extinction of the transitional forms between two different types 

 derived from a common ancestor by gradual modifications. In either case 

 there is room for individual judgment in the delimitation of species, accord- 

 ing as the differences between the two types are greater or smaller. We say, 

 "A species is a perennial succession of like individuals." But how nearly 

 alike must they be. No two individuals are exactly alike, and the extreme 

 differences possible between two individuals of the same species may be 

 greater than those between two individuals of different species. In other 



