Amphicarpcea morn 



tnent ; but really there was little difference in the rapidity. 

 All formed irregular small circles in an hour or an hour 

 and a quarter. 1 do not feel thoroughly satisfied with the 

 methods adopted in observing the axillary shoots, and I 

 trust in future studies to remedy these defects. 



Histology of the Stem. 



In general the stem exhibits the structure of a typical Dico- 

 tyledon. Plate XXIV, Fig. [, shows the transverse section of 

 a very young stem of a plant about six inches high; the epi- 

 dermal cells have the outer walls slightly cuticularized. 

 Numerous rows of cells constitute the cortex. Next may 

 be distinguished one row of flattened, slightly thickened 

 cells which form the bundle sheath. About ten vascular 

 bundles surround the central fundamental tissue ; the pro- 

 toxylem is well marked. Among the protoxylem cells 

 and spiral tracheae are found tannin canals. In the phloem 

 numerous sieve cells with comparatively large plates are 

 seen ; here, too, among the companion cells appear tannin 

 canals ; usually one in the phloem of each bundle. Small 

 areas of hard bast are seen forming in the region bordering 

 directly upon the bundle sheath. 



In sections of an older stein (Fig. 2), we find that the hard 

 bast has developed considerably, forming an almost complete 

 ring. The xylem appears to push down into the phloem, 

 forcing it aside into two nearly distinct patches. Tannin 

 canals are now more numerous than in the young phloem, 

 three or more being present in each area. From study of 

 longitudinal sections the component elements of the sec- 

 ondary xylem are found to be wood cells, pitted vessels and 

 tracheids with reticulated walls. In the cells of the bun- 

 dle-sheath, just outside of the hard bast, are found pris- 

 matic crystals of similar appearance to those met with in 

 the leaf and other portions of the plant. Their appear- 

 ance will be described more minutely in later pages. At 

 present their position and development in the plant de- 

 mand attention. 



