II LEAF STRUCTURE OF JOUVEA AND OF ERAGROSTIS 



OBTUSIFLORA. 



(Plates VIII and IX.) 



By Miss E. L. Ogdex. 



JOUVEA. 



Two species of the genus Jouvca have been distinguished — J. irilosa 

 (Presl.) Sciibu. and J. straininca Fourn. In the former species no dis- 

 tinction can be made in habit or in character of leaves between $ and 

 3 plants, and to these the i i^lant of J. straminea bears a close resem- 

 blance. Their leaves are rigid, closely conduplicate throughout their 

 entire length, and terminate in a sharp, thorn-like point. The S plant 

 of J. stra7ninea, which is perhaps not identified beyond the possibility 

 of a doubt,^ usually has smaller and less rigid leaves tban those of the 

 other species, yet in respect both to size and rigidity the leaves of all 

 vary within wide limits, and render this distinction of little impor- 

 tance. In J. straminea the plants of diiferent sex are strikingly unlike. 

 The pistillate plant is slender with long, soft leaves that are flat for the 

 greater part of their length and slightly involute only toward the apex. 



The points of resemblance presented by ijlants of different specievS as 

 well as the marked difference between tbe i)lants of different sex of the 

 S])ecies strain hi ea vGuder a close examination of their structure of much 

 interest. It is, furthermore, of mu(;h interest to compare with Jonna., 

 the leaf stiucture of Eragrostis ohtnsijiora (Fourn.) Sciibn., a peculiar 

 grass of the same region, which was at first suspected to be a new spe 

 cies of the genus in question. And since Jouvea itself has been referred 

 to Distichlis, a comi)arative study is added of i>. sjncata (Linn.) Greene, 

 as a representative of the latter genus. 



These plants are all inhabitants of dry regions. Jouvea and Era- 

 grostis obtusifiora belong to the sandy deserts of Arizona and Mexico, 

 while J), spicata has a wider distribution. They may therefore be 

 expected to show similarity in all characters of structure that are 

 especially affected by conditions of climate and soil. At the same time 

 ])]ants of the same species growing under diftereut conditions will vary 

 much in regard to the presence and state of development of structures 

 ujton which ability to resist drought depends. 



From an anatomical ])oint of view the leaf of Jourea pilosa is inter- 

 esting both on account of its individual peculiarities and on account of 



' Bull. Ton-. IJot. Chib., ^'ol. XXIII, No. 4, Ai)ril, IS'JO, Grass Notes by F. Laiiisoii- 

 Scribiier. 

 12 



