GRASSES OF IOWA. 23 



gives the leaf additional strength. The number and character 

 of the bundles varies in different species of grasses. In Spo- 

 robolus heterolepls, Miss Emma Sirrine and Mrs. Hansen found 

 that the mid-rib consists of a single mestome bundle.* 



This bundle is surrounded on the upper side by chlorophyll 

 bearing parencbyma, while the lower side contains stereome. 

 The mestome bundles to the right and left of the mid-nerve 

 are entirely closed, that is entirely surrounded by chlorophyll 

 bearing parenchyma. There are three types of mestome 

 bundles in this species as follows, the mid-nerve with stereome 

 on the lower side which is in contact with leptome or the 

 second with stereome en lower and upper sides in contact with 

 leptome, and third, entirely closed. These alternate with 

 those having stereome on upper and lower surfaces. The 

 leaves terminate with one closed mestome bundle. The 

 uncolored parenchyma of the leaf is in immediate contact with 

 tbe stereome. This is most conspicuous near the mid-nerve. 

 The chlorophyll parenchyma may be divided into two parts, 

 first, large parenchyma cells, which surround the bundles, 

 and, second, to the outside of these, elongated cells in one or 

 more rows. This species represents a type intermediate 

 between plants adapted to very dry climates and one adapted 

 to somewhat moister conditions. Mrs. Hansei has described 

 the structure of a typical xerophytic plant, Festucu tenella.] 

 In this species the mestome bundles number twelve and are of 

 three types. First, primary, open both on inferior and 

 superior surfaces of leaf, i. e. , those which have hadrome and 

 leptome respectively in contact with stereome, either in 

 direct contact or are separated from it by several rows of thin- 

 walled parenchyma cells. Second, the secondary type. These 

 are entirely surrounded by chlorophyll-bearing parenchyma. 

 Third, intermediate type. These open inferiorly. Only one 

 bundle of primary type occurs and this is in the mid-nerve. 

 The leptome and hadrome are in direct contact with each 

 other. The leptome is separated from the stereome by thin- 

 walled parenchyma cells. A considerable development of 

 thin-walled parenchyma cells occurs above the mestome 



♦Some anatomical studies of leaves of Sporobolus and Panicum. Proc. Ta. Acad. 

 Scl.. Des Moines. 3: 151. pi. (>. f. 1-3. 1896. Conir. Bot. Dapt. la. St. Coll. Agrl. Mechanic 

 Arts. 1. 



+ A comparative study of th'i leaves of LoUum, Festuca. and Bromus. Proc. la. 

 Acad. Scl., Des Moines. 4: 127. 1897. Contr. Bot. Dept. la. St. Coll. Agrl. and Mechanic 

 Arts. i. 



