306 



SCIENCE 



[N. S. Vol. XLVII. No. 1213 



imique in themselves which serve to illumi- 

 nate general biological principles. One can 

 not for a moment doubt that in some way 

 or other the processes of existence have 

 worked striking modifications in the para- 

 sitic forms when one compares them with 

 their free-living relatives and scans the 

 changes which take place in the individual 

 development. Not even the most extreme 

 conservative would wish to maintain that 

 the parasite was an original product, or 

 would hesitate to grant that it had become 

 adapted to its present mode of life. Yet 

 more extraordinary and far-reaching struc- 

 tural modifications icould hardly be asked 

 for or found than those which are evident 

 in the parasitic organisms. Nor would it 

 be easy to conceive more intricate or more 

 precisely balanced relations than those 

 which exist between some parasites . and 

 their hosts. The development, modifica- 

 tions and habits of the parasite have been 

 coordinated with the conditions of exist- 

 ence in the host in strikingly precise fash- 

 ion. Investigation has as yet only begun to 

 work out the adjustments which have arisen 

 independently and in great variety in dif- 

 ferent species and groups of parasitic spe- 

 cies. The field is one that offers unusual op- 

 portunities at the present time to the in- 

 vestigator. 



"We do not know how far an intimate 

 study of these problems may carry us 

 towards the explanation of the process of 

 evolution in free-living organisms. There 

 is reason to think that the change has been 

 more rapid as well as more radical among 

 parasitic species. And if so, the study of 

 this problem at this point may be expected 

 to throw welcome light on the factors that 

 lead to structural changes in living organ- 

 isms. Any such study will certainly serve 

 an important purpose in broadening the 

 human mind and encouraging it to seek the 



solution of the problems of existence more 

 vigorously than it has even done as yet. 



The outlook for the future constitutes 

 no less than the achievements of the past, a 

 real contribution to the cause of human 

 progress. Henry B. Ward 



IjNivERSirY or Illinois 



THE INDIGEN AND CULTIGEN 



If an author were to prepare a flora or 

 manual of cultivated plants in any country, 

 he would come hard against the fact that he 

 deals with two gentes or types of species. 



One gens has recorded origin, with the typi- 

 cal form weU. recognized and probably repre- 

 sented by a " type specimen " in the herbarium 

 of the person who " founded " the species. It 

 in an indigen of known habitat. 



The other gens is a domesticated group of 

 which the origin may be unknown or indefinite, 

 which has such characters as to separate it 

 from known indigens, and which is probably 

 not represented by any type specimen or ex- 

 act description, having therefore no clear taxo- 

 nomic beginning. I trust I may be pardoned 

 for calling such species or group a cultigen. 



A good example of the cultivated indigen is 

 Thuja occidentalis. Although there are many 

 horticultural forms, their relationship is un- 

 derstood, we are familiar with the species in 

 the wild, and we have the whole case before 

 us. The variations under domestication are 

 indeed great, but we readily range them with 

 what we call the species itself. 



A good example of the cultigen is Zea Mays. 

 We know neither its country nor its origin. 

 It is widely variable. If a botanist had be- 

 fore him good material of all these variations, 

 I do not know what one of them he would 

 take as " the type." It is a composite gens, 

 with no clear taxonomic center from which 

 variations diverge. 



Here we have two classes of facts, with no 

 adequate way of expressing one of them in 

 taxonomy. 



If Zea Mays were an isolated case we could 

 treat it as an exception. I have before me 

 a list of one or two hundred comparable cases. 



