674 MINNESOTA BOTANICAL STUDIES. 



XL. ON THE STEM ANATOMY OF CERTAIN 

 ONAGRACEAE. 



Francis Ramaley. 



Introduction. — During the past year a comparative study has 

 been made of the minute anatomy of the stem in a considerable 

 number of genera of Onagraceae. The plants investigated are 

 all of the tribe Onagreae, a group, the members of which show 

 strong natural affinities. 



The chief purpose of the paper is to give an accurate account 

 of the stem anatomy in the plants examined, together with a 

 brief historical summary of the literature bearing upon the 

 points of greatest interest. For the sake of simplicity this 

 historical account has been greatly compressed and divided 

 into separate sections. References to text books have not 

 been given. 



The nomenclature used is that of the Check List. 1 This has 

 been followed merely for convenience and because it has seemed 

 best, in a purely morphological paper, to avoid nomenclatural 

 difficulties. Only plants enumerated in the check list have been 

 examined. These are all indigenous, and, as a rule, restricted 

 to North America, although Onagra biennis was, according to 

 Raimann, 2 introduced into Europe at the beginning of the sev- 

 enteenth century and is now a common roadside weed. 



Taxonomic value of anatomical characters. — The import- 

 ance of histological characters in drawing specific descriptions 

 has been discussed at some length by Vesque. 3, 4 In his mono- 

 graph on the Guttiferae 5 he makes continual use of microscopic 

 differences for purposes of classification. Weiss, 6 in an article 



1. Mem. Torr. Bot. Club. 5:233-230. 1894. 



2. Onagraceae in Engler and Prantl, Nat. Pfl. Fam. 3: Abt. 7. 199. 1893. 



3. Vesque, J. De la concomitance des characteres anatoniiques et organograph- 



iques des plautes.— Comptes rendus. 96: 1866-1868. 1883. 



4. Vesque, J. L'anatomie des tissus appliyue'e a la classification des plantes. — 



Mem. II, Nouv. Arch, du Mus. d'hist. natur. II. 5:291-387. 1883. 



5. Vesque, J. Guttiferae. — DeCandolle. Monographiae Phanerogamarum 8. 



1893. 



6. WeUs, J. E. Beitraege zur Kenntniss der Kork-bildung. Denksehriften derKgl- 



Bayerischen Botan. Oes zu Regensburg. 6 : 1890. 



