4 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



Edward Palmer, C. C. Parry, Henry Pittier, C. G. Pringle, C. A. 

 Purpus, B. P. Eeko, J. N. Rose, J. N. Rovirosa, H. H. Rusby, W. E. 

 Safford, H. C. Seaton, J. G. Schaffner, Arthur Schott, C. L. Smith, 

 L. C. Smith, C. H. T. Townsend and C. M. Barber, Charles Wright, 

 W. G. Wright, L. J. Xantus. 



SPECIES INCLUDED. 



It is manifest that the group here chosen for treatment is an 

 artificial one. It is impossible to draw a sharp line between the 

 woody and herbaceous plants, although in the vast majority of cases 

 such a classification is easily made. Many truly woody plants are 

 so small that they are not looked upon conmionly as shrubs, and 

 many herbaceous plants become so large as to remind one of small 

 trees. Plants which are essentially annuals, and which in regions 

 where freezing temperatures occur never live more than one season, 

 may in tropical regions develop more or less woody stems. More- 

 over, in herbarium specimens, which as a rule consist merely of 

 terminal portions of branches, it is often impossible to conclude that 

 a plant is a shrub except from analogy or from information fur- 

 nished by collectors. The writer would have preferred to treat 

 only of the trees of Mexico, which are far less numerous than the 

 shrubs and would have required less space for their elaboration; 

 but the separation in the herbarium of trees and shrubs involves still 

 greater difficulties than the separation of woody and herbaceous 

 plants. We have so little published information regarding the size 

 of Mexican plants, and most collectors show such an aversion to 

 furnishing notes concerning their collections, that the classification 

 of woody plants as trees and shrubs is evidently quite impracticable 

 with our present knowledge. The writer's policy as to the species 

 to be included has been a liberal one, and although it is possible that 

 some species have been omitted which should have been included. 

 it is certain that their number is small. On the other hand, many 

 species have probably been included which should have been omitted, 

 but this fact will increase rather than detract from the usefulness 

 of the work. Some species have been listed as shrubs, rather against 

 the judgment of the writer, because of data reported by collectors. 



The statements given here concerning size are the best that can 

 be compiled from published notes and from information furnished 

 by collectors' labels. ^ The information available is not so complete 

 as is desirable and in some cases may be misleading. It has not 

 been the intention to publish a descriptive inaiuial. and the brief 

 descriptive notes given under most of the si)ocies arc intended merely 

 to supplement the keys and to indicate the most striking features of 

 each species. Keys are gi\'en for the determination of genera and 



