ROOTS. 97 



ROOT OF A DICOTYL PLANT. Make cross-sections of the root 

 of the May Apple (Podophyllum peltatum) and stain in phloro- 

 glucin. In the center of the section will be found the bundle, 

 which in this plant is usually pentarch, i. e., has five xylem rays. 

 The rays are wedge-shaped, with the broad ends towards the 

 center. At the outer narrow ends of the rays the ducts are 

 smaller in diameter, but are much larger at the broad ends and 

 mostly scalariform. The central portion of the bundle is made 

 up of parenchyma cells, among which may be a few scattered 

 ducts. 



The phloem masses lie between the xylem rays, towards their 

 outer ends, and are separated from them by several layers of 

 parenchyma cells. The cells of the phloem have glistening 

 walls and may be told by these. The bundle is enclosed by an 

 endodermis of elongated cells, which are thin-walled, as is usual 

 in dicotyl plants. Immediately next to the endodermis are two 

 layers of cells, larger in diameter than the cells of the endo- 

 dermis or of the phloem and containing some fine-grained starch. 

 These cells are known as the pericambium or phloem-sheath. 

 The cells have the power of multiplication and root branches 

 have their origin from them, opposite the xylem rays. 



The area outside of the bundle is filled with parenchyma cells 

 densely filled with starch grains. 



ROOT OP A MONOCOTYL PLANT. Make sections of the root of 

 Yellow Lady's Slipper (Cypripedium pubescens), a monocotyl 

 plant, and stain with phloroglucin. The xylem rays are about 

 eight in number, longer and better developed than in the pre- 

 vious case. They meet at the center of the section, where there 

 are numerous large ducts and smaller thick- walled cells. The 

 ends of the rays are surrounded by thick-walled narrow cells 

 which reach out to the endodermis, interrupting the pericam- 

 bium layer in places. The phloem masses lie between the rays ; 

 the walls of the cells are thin and glistening. The endodermis 

 is peculiar in that the cells opposite the phloem masses have 

 their radial and inner walls much thickened, giving to these 

 parts the appearance of a crescent, while the outer walls remain 

 thin. The other cells of the endodermis opposite the xylem rays 

 are thin-walled. This is a peculiarity of the endodermis of 

 monocotyl roots. Make a drawing of the bundle. 



Compare with the section of Cypripedium, one from the root 

 of the corn plant, which is also a monocotyl. There are about 

 fifteen xylem rays, somewhat like those of podophyllum in ap- 

 pearance. They do not reach to the center of the bundle. This 

 is filled up with parenchj^ma cells, in which there is a circle of 

 five very large vessels. 



The roots of monocotyls undergo very little change as they 

 grow older, but while the young roots of dicotyls present the 

 appearance described under the root of Podophyllum, the older 



