34 GRASSES OF IOWA. 



mid-nerve, leptome and hadrome are well developed. The 

 pitted vessels are large. Stereome is well developed on infe- 

 rior and superior surfaces of the bundles. In the mid-nerve, 

 leptome and hadrome are separated from eich other by thick- 

 walled cells. The cells in leptome are somewhat more thick- 

 walled than in hadrome. " 



Mr. C. B. Weaver's study* of Andropogon provincialis shows 

 the presence of four types of bundles, viz. : first, mid-nerve; sec- 

 ond, entirely closed; third, open, and fourth, larger secondary 

 bundles with stereome both above and below. 



" The mid-nerve consists of three large bundles open above 

 and below. The central bundle is but little larger than the 

 secondary bundles. In the hadrome occur the conspicuous 

 pitted and spiral ducts. The chlorophyll-bearing parenchyma 

 cells surrounding the larger bundles are not as conspicuous as 

 those of the smaller mestome bundles. The stereome above the 

 mid-nerve is well developed and is wider than the middle larger 

 bundle; while opposite on the lower side of the leaf occur but 

 few stereome cells, and these latter are in direct contact with 

 the epidermal cells. The cells composing the leptome portion 

 of the mid-nerve bundle are uniform in size. The uncolored 

 parenchyma cells which occur below and to the side of the 

 mid-nerve bundle, are large. These cells are in contact with 

 the three large bundles of mid-nerve. The smaller mestome 

 bundles on either side of the mid-nerve occur close together. 

 The chlorophyll-bearing parenchyma cells surrounding these 

 are conspicuous. These bundles are not uniform in number on 

 both sides the mid -rib, which goes to show that the development 

 of the leaf is unequal. On each side of the mid-nerve occur 

 four of the larger secondary bundles. The edges of the leaf 

 are provided with stereome. The stereome about the cells varies 

 in the number of cells. The cells of the mesophyll occur as 

 dense masses with numerous intercellular spaces. They vary 

 in shape from elongated to spherical. An occasional small 

 trichome may be seen." 



It may be interesting to compare the above structure with 

 that of a typical woodland grass, and for that purpose we may 

 take Bromus breviaristatus. According to the researches of 

 Miss Emma Sirrine,t the mestone bundles number forty-one. 



*An anatomical study of the leaves of some species of the genus Andropogon. 

 Proc. la. Acad. Scl , Das Moines. 4: 133, 1897. Oontr. Bot. Dept. la. St. Coll. Agrl. and 

 Mechanic Arts. 4. 



+A study of the leaf anatomy of some species of the genus Bromus. Proc. la. 

 Acad. Scl., Des Moines. 4: 135. pi. 4, f. 1; pi. 7, /. 7, 1897. Oontr. Bjt. Dept., la. St. 

 Coll. Agrl. and Mechanic Arts, 4. 



