100 MINNESOTA BOTANICAL STUDIES. 



Concerning the structure of the stele it is to be noted that in 

 the hypocotyl it is quadrangular; it has but four vascular 

 bundles instead of from eight to twelve and there is no stereom, 

 while in the epicotyl a crescentic mass of stereom borders each 

 phloem bundle. 



CALYCANTHACE^E. 



Butneria florida. 

 Structure of Hypocotyl. 



The epidermis consists of cells which are nearly square in 

 cross section. They soon become more or less broken, owing 

 to the early formation of cork. A few short, pointed, uni- 

 cellular hairs are present. 



A true hypoderma becomes differentiated late in the season. 

 About three or four of the sub-epidermal layers of cells become 

 collenchymatous. The cortex has about twenty layers of cells 

 all approximately the same size. Intercellular spaces abound. 



The endodermal cells are but slightly smaller than those of 

 the cortex. The endodermis remains more or less distinct until 

 the close of the first year. Starch grains are very small. A 

 few are found in the endodermis, but no starch is present in the 

 other parts of the hypocotyl till late in the season, when it is 

 found in great abundance throughout all the parenchymatous 

 tissues. 



The stele is somewhat quadrangular. There are four xylem 

 bundles and four principal phloem bundles. These are situated 

 in the angles of the stele. There are also some small phloem 

 areas. Their location will be seen by reference to the diagram. 

 The phloem and xylem soon form narrow, closed zones. The 

 former is most developed at the original angles of the stele. 



It is .stated by De Bary [1884], that in the seedlings of Caly- 

 canthaceae a transverse section of the hypocotyl shows six bun- 

 dles. In the plant under investigation, the present writer found 

 this to be true only for the upper end of the hypocotyl where the 

 cortical bundles, to be mentioned later, are separating and pre- 

 paring to leave the stele. This appearance is, of course, only 

 seen after the fusion of the primaiy xylem bundles in pairs, 

 and before complete rings of phloem and xylem are produced. 



Toward the upper limit of the hypocotyl there is present a 

 small stereom bundle at each of the four angles of the stele. 



