112 ERYTHEA. 



to light iu the course of several years' study, especially as an ex- 

 cellent opportunity had been given to examine Dr. Engelmaun's 

 types and unpublished notes." 



It may be doubtec^. whether the benefits, derivable from the bring- 

 ing together of scattered descriptions^ is at all commensurate with 

 the confusion caused by the publication of these notes, which every 

 botanist knows Dr. Engelmann^would never have allowed to appear. 

 If Engelmann had lived, they might have become intelligible to his 

 trained mind, as he would have received unnamed all the material 

 collected by American botanists and he would have been in corre- 

 spondence with Dr. Weber. The botanical world would have been 

 spared a good many synonyms and^what is infinitely worse, a lot of 

 "new species" vaguely characterized and vaguely localized, which 

 only an exhaustive knowledge of an extensive region can determine 

 with certainty. It is somewhat the custom, and usually deservedly 

 so, to discredit the species, so called, which occur in trade or agri- 

 cultural journals, but no one of them could have done worse than 

 to publish such a diagnosis as that of Opuntia tesajo, to which the 

 honored name of Engelmann has been appended. The motives of 

 the editor were no doubt kindly, but his work only emphasizes the 

 impropriety of making a dead man responsible for names published 

 at any considerable interval after his death, more particularly 

 where the work of a specialist is edited by some one untrained in 

 the specialty. 



In the researches necessary to the preparation of this paper, 

 Professor Trelease, of the Missouri Botanical Garden, has been 

 extremely kind in affording me an opportunity to study and com- 

 pare Gabb's types with living forms, nearly all of the Baja Califor- 

 nia species being now represented in our garden. Dr. Weber also 

 responded generously to our request for portions of his types. In 

 this way a considerable number of the species can be made out 

 with certainty, and when they have attained some size and borne 

 flowers and fruit, can be more satisfactorily compared with the 

 species of Mexico proper. 



MAMILLARIA. 



This large genus appears to me divisible into four well-marked 

 sub-genera or sections, better and more clearly separable from each 



