682 MINNESOTA BOTANICAL STUDIES. 



eter. In longitudinal section they are seen to be greatly- 

 elongated, often from 100 to 250mik. in length. In Kneifna 

 glauca and Kneiffia pumila no crystal sacs were observed. 



The differences of different stems shown in the sub-epider- 

 mis are in the relative amounts of sclerenchyma and col- 

 lenchyma, the thickness of the parenchymatous zone and the 

 presence or absence of crystal bearing cells. In some cases 

 the same species will afford as marked differences, in different 

 plants, as are found in the most widely separated species which 

 were examined. 



Endodermis. — This is, at least in herbarium material of any 

 considerable age, very indistinctly differentiated from the ad- 

 jacent cells. It cannot ordinarily be distinguished except from 

 its position as just outside the groups of paricyclic stereome. 

 The cells, seen in cross section, appear elliptical or flattened 

 in outline. 



Pericycle. — This is in all cases heterogeneous and a number 

 of cells in thickness. The cells are usually somewhat flattened, 

 ellipsoidal in shape, the longitudinal diameter commonly the 

 longest, the radial the shortest. Toward the outer boundary 

 of the pericycle are groups of thick- walled fibrous cells These 

 cells are often 200to400mik. long; they have a narrow lumen. 

 In cross section they appear five or six-sided. The middle 

 lamella is usually quite distinct. The cell walls are ordinarily 

 of unmodified cellulose. In some of the sections they present 

 a somewhat marked lignin reaction. Apparently this lignifica- 

 tion is not confined to or characteristic of any one or greater 

 number of species. The stereome cells occur, in most cases, 

 in patches of considerable size, three or four rows broad in a 

 radial direction, the patches separated from each other by 

 parenchyma (e. g., Onagra biennis, Anogra pallida, Oenothera 

 rhombipetala). Sometimes this stereome area is very narrow, 

 but a single cell broad, and forms a continuous or nearly con- 

 tinuous closed ring. 



The cork is of pericyclic origin, essentially similar in all the 

 species examined. It is made up of flattened rectangular pris- 

 matic cells of two sizes, arranged in alternating layers. The 

 large cells have a radial diameter about four times as great as 

 have the small ones. The latter commonly carry a brownish 

 pigment. In Anogra pallida this pigment is, for the most part 

 absent; this is also the case occasionally in other species. In 

 the species named the cork in older parts shows a tendency to 



