BLAKE: REVISION OF THE AVOCADOS 9 



BOTANY. — A preliminary revision of the North American and 

 West Indian avocados (Persea spp.). S. F. Blake, Bureau 

 of Plant Industry. 



For several years Wilson Popenoe, of the Office of Seed and 

 Plant Introduction, has been engaged in the collection of the 

 various forms of the avocado, or "alligator pear," which are 

 found in Mexico and Central America. Man)^ new and valuable 

 forms have been introduced into the gardens maintained by the 

 Office, whence they are being distributed among horticulturists, 

 and a considerable amount of herbarium material has been ac- 

 cumulated. This material, which has recently been put into 

 my hands for study, is sufficient, in connection with that already 

 in the U. S. National Herbarium, to permit a fairly satisfactory 

 preliminary treatment of the forms of the avocado which occur 

 in Mexico, Central America, and the West Indies. Mr. Popenoe 

 is about to extend the field of his investigations by a two years' 

 trip in Central and South America, in which it is hoped material 

 will be secured to settle the status of one or two South American 

 forms, at present too poorly represented in our herbaria to be 

 disposed of definitely. In the meantime it is desirable to put 

 on record the information already obtained as to the relationship 

 of the forms north of the Isthmus. 



The latest systematic treatment of Persea americana and its 

 relatives is that of Mez (1889),^ in his monograph of the Ameri- 

 can Lauraceae. Mez recognizes, in the small group made up of 

 the avocados, two species, Persea gratissima Gaertn. f. (Laurus 

 persea L.) and P. floccosa Mez. Of P. gratissima two varieties 

 are recognized in addition to the type, P. gratissima schiedeana 

 (Nees) Meissn. and P. g. drymifolia (Schlecht. & Cham.) Mez. 

 In a later publication Mez^ has recognized the priority of the 

 name Persea americana Mill. (1768) over P. gratissima Gaertn. 

 f. (1807), the name by which the common avocado has generally 

 been known in literature. 



Mr. Popenoe,^ as a result of his extensive field acquaintance 



' Jahrb. Bot. Gart. Berlin 5: 145-148. 1889. 



2 Arb. Bot. Gard. Breslau i: 113. 1892. 



' In Bailey, Stand. Cycl. Hort. 5: 2556. 1916. 



