38 - NINTH REPORT. 



and if after many generations they continue to exhibit constant differences 

 they are to be regarded as two species. On the contrary if they show the 

 same characters imder the same conditions, they are one species. Such a 

 method of determining whether one has a new species or not involves an 

 enormous amount of labor, and a great deal of time. It is not in favor with 

 the systematists who work with the higher plants. Nevertheless there is 

 an increasing recognition among botanists of the necessity of physiological 

 work even in those fields of research that have in the past been dominated 

 by morphology alone. 



SjLich experiments might help to decide the c[uestion whether the so-called 

 alpine species have been constant since the glacial period, as de Vries sup- 

 poses they must have been, or whether, as seems possible, similar combina- 

 tions of climatic conditions, operating in widely separated regions such as 

 the alpine region of central Europe and the high latitude of Norway, have 

 produced species of similar form. It does not even seem necessary to as- 

 sume that the parent species of the alpine form has been the same in these 

 widely separated regions. De Yr'ies has pointed out that species sometimes 

 over-lap by what he calls transgression variations. Klebs has shown that 

 in one species of Sempervivum he could produce nearly all the characters 

 found in the other species of the genus. Is it not therefore possible that the 

 continuation of conditions of soil, temperature, moisture and light charac- 

 teristic of the alpine region could produce a type varying al)out a new aver- 

 age, which lies near one of the extremes of the fluctuating variations of the 

 parent species. 



If this new average should be established within the limits of the trans- 

 gressive variations of the two species, one of which existed in northern 

 Europe and the other in central Europe, we should have the production of 

 similar types, the alpine and arctic type, in widely separated regions and from 

 different parent species. The characters of the new type are not "fixed" in 

 the sense of being due to iidieritance, l^ut only in the sense that they are a 

 response to a particular combination of external factors, and this coml^ina- 

 tion is constant in the given regions. Such a view of the origin of alpine 

 types is not merely of theoretical interest, since the application of the 

 physiological method gives the means of reaching more or less definite 

 conclusions. 



De Vries and others have pointed out that the species of the manuals and 

 the systematic botanists are in large part composite or collective species and 

 not simple or elementary species. In his view the latter differ from their 

 parent species by ^lew characters not by modifications of old ones. The new 

 characters are inheritable as soon as they a]ipear, and are not regulated by 

 the external conditions in which the adult plant lives. 



If Mac Dougal's work stands the test of repetition physiological experiment 

 may open up a new field in investigating the origin of species. One method 

 of applying physiological experiment to determining the limits of species 

 has just been discussed. But other applications of this method are possible. 

 It is well known that cross fertilization generally takes place only between 

 closely related species of plants, rarely between genera. When attempts 

 are made to cross species remotely related, either the pollen does not grow 

 upon the stigma of the strange specie, or fertilization of the egg does not 

 take place, or if seeds develop the resulting hybrid is sterile, not being able 

 to prodvice seeds for its propagation. What lies at the basis of these physio- 

 logical differences is still obscure. It is probable that enzymes, toxins, or 

 other chemical substances play a part. But whatever the explanation, the 



