114 CONTRIBUTIONS FEOM THE NATIONAL HERBARIUM. 



there may be several specimens from which the type must be selected 

 by comparison with the description (Panicum barbulaturn Michx., 

 page 148). These and other difficulties complicate the study and 

 make it necessary to examine carefully all the evidence. This evi- 

 dence not infrequently shows that a species has been misunderstood. 

 The original description may be insufficient to identify the species, 

 but the identity can be established by the type specimen (Panicitm 

 nitidum Lam., page 148). Tradition may have attached a name to 

 one species, while the description and the type specimen show that 

 the name belongs to another species (Cenchrus tribuloides L., page 127; 

 Agrostis aspera Michx., page 150). 



In the following account I have considered each case upon its 

 merits and have presented the evidence upon which I have based 

 my decision. It will be seen that usually the apparent difficulties 

 disappear and we are able to determine the specimen the author 

 had chiefly in mind when he wrote the description. The earlier 

 authors, especially Linnaeus, frequently cited descriptions or plates 

 which they considered as referring to the same plant they were describ- 

 ing. Linnaeus even based his binomial upon the description or plate 

 of another author. If an author quotes the diagnosis of a species 

 described by another author and gives a name to this, but has no 

 description of his own, the type of the older author becomes the 

 type of the later (Panicum capillarc, L., page 118). Linnaeus often 

 gave binomial names to species described by others. But if Linnaeus 

 wrote a description and there has been preserved a specimen which 

 the evidence shows must have been seen by him when he drew up 

 the description, this specimen is the type, and not the specimen 

 which is the basis of the synonym (Panicum latifolium L.,page 118; 

 Paspalu m pa niculatum L. , page 116). The danger of placing too much 

 weight upon cited synonyms as evidence is shown by the fact that 

 Linnaeus sometimes cited a given Sloane plate under different species 

 in different works or even in the same work (Panicum sanguinale 

 L., page 117); or the synonyms may be quite different from the species 

 under which they are cited (Andropogon nutans L., page 125). 



Fortunately the grasses left us by the older authors, though often 

 fragmentary, are in a satisfactory state of preservation, and it is 

 usually possible to determine their identity with certainty. 



THE AMERICAN GRASSES DESCRIBED BY LINN^US. 



The herbarium of Linnaeus, preserved at the rooms of the Linnaean 

 Society of London, Burlington House, Piccadilly, contains most of 

 his types. In the following article I have considered only those 

 species based wholly or in part upon American material, nearly all 

 of which was furnished by Kalm, Gronovius, Sloane, or Browne. In 

 the case of Old World species the specimens preserved by Linnaeus 



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