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THE AMERICAN NATURALIST [Vol. XLII 



Even a casual survey of the practises in species- 

 making during a century or more shows little or no 

 uniformity of criteria or results. A comparison of 

 methods in the different plant groups is even more stri- 

 king. This lack of uniformity is found not only in the 

 work of botanists in general, but even in the work of 

 the same botanist. The consequences in the form of 

 unequal and invalid species have been almost innumer- 

 able. This is particularly true of the fungi. To one 

 familiar with them, it seems certain that the number of 

 valid species is considerably less than half the number 

 published. Attempts to guide the descriptive botanists 

 and to make species more definite and uniform have not 

 been wanting. A few of these have been noted, in order 

 to show how little effect they had, even upon their own 

 authors, and how utterly impossible of application they 

 are without the test of experiment. 



The criteria proposed by Ray were permanence of 

 form and appearance, and non-fertility with other species. 

 This appears to be little more than an attempt to justify 

 the practise prevalent under the dogma of special crea- 

 tion. Mere observation could give little support to either 

 criterion, and the thought of experimental support was 

 scarcely dreamed of. As a pioneer in evolution, La- 

 marck gave a definition of the species, which would be 

 expected to warrant more than passing interest. He 

 defined a species as a ' 'collection of similar individuals 

 which are perpetuated in the same conditions as long 

 as their environment is not changed sufficiently to bring- 

 about variation in their habits, their character or their 

 form." It is clear that the whole value of this definition 

 depends upon the significance given to the word varia- 

 tion. Lamarck, in his strong feeling for adaptation, hit 

 upon the two essential facts, environment and variation, 

 but his application of these criteria was purely academic. 



It is a significant fact that Darwin should have written 



