558 WEED FLORA OF IOWA 



tegument excepting in the base of the hair cells. The palisade 

 cells, c, are narrow for their length. The cell cavity is not promi- 

 nent and the nodosity is inconspicuous. The light line is narrow 

 and occurs near the outer end of the palisade layer. The sub- 

 palisade portion, d, is made up of two layers of light brown cells. 

 They are symmetrical and elongated tangentially. 



Measurements, seed coats, 147m ; outer integument, 13m ; palisade 

 layer, 96m ; subpalisade, 38m. 



Shoo-fly (Hibiscus trionum L.)- 



P. H. Rolfs has made a study of H. militaris, the microscopic 

 structure of which species closely resembles that of R. trionum. 

 The dark grayish seeds are roughened with tubercular processes, 

 which contain the "seed hairs." The seed hairs consist of cells 

 somewhat longer than broad beginning with a broad base, ex- 

 tending into a several-celled trichome, the terminal portion larger 

 than remainder of cell. These hairs contain a yellow pigment. 

 The Malpighian cells occupy about one-half the thickness of the 

 testa, the cuticle is well developed, the light line is near the upper 

 portion of the cell. The cell cavity is spindle-shaped and near 

 the middle of the cell. The remainder of the testa consists of a 

 subpalisade portion of parenchyma cells carrying a brownish pig- 

 ment; underneath it, larger thin-walled cells; walls brownish, a 

 compressed marrow, brownish layer, the nucellus, n. This is fol- 

 lowed by the squarish cells of the endosperm. 



Common Mallow (Malva sylvestris L.). 



The surface of M. sylvestris is rough in appearance. The second 

 layer, o, of the outer integument, a, has been compressed into a 

 thin layer and seems to have no definite arrangement. The outer 

 layer, a, has been elongated radially. In places, these elongated 

 cells have divided forming a double layer of cells. There is no 

 brown coloring matter in this integument nor is there any between 

 the integuments. The palisade cells, c, are clear ; the walls thick. 

 The cell cavity occupies about one-third the length of the cells, 

 the lower end reaching to the middle. The nodosity is promi- 

 nent. Below the cavity the cells are clear, almost transparent. 

 The subpalisade portion, d, is usually made up of two layers, at 

 some places only one, of large dark brown cells. 



