Ra77ialey : iiypocotyl and epicotvl in woody pi.ants. 89 



bitUy Tagelcs^ Convolvulus and Mirabilis, or, the rhizelle, as in 

 RanunculacCcE, Cruciferie, Caryophyllaceae, Chenopodiaceae, 

 Umbellifertc, Rubiaceas and Conifer^e, or by a combination of 

 the growth of botii as in Buojiymus. 



The designation of certain regions as tigelle, rhizelle and 

 tigellaire does not seem to the present writer a matter of great 

 importance in the plants which he has studied, for in them these 

 regions are by no means sharply differentiated. Further obser- 

 vations and references to the work of Flot mentioned above 

 are given in the pages which follow. 



In the special portion of the present work will be found de- 

 scriptions of the structure of hypocotyl and epicotyl in the 

 various species examined. Accompanying each description is a 

 diagram of the cross section of the hypocotyl when the seedling 

 is in the first stage previously described, and diagrams of both 

 hypocotyl and epicotyl of the second and third stages. In these 

 diagrams stereom is black, xylem is dotted, cortex, phloem, 

 pericycle and the pith are white. The endodermis, when dis- 

 tinct, is indicated by a single line as is also the epidermis and 

 the boundaries between the various zones. In each figure the 

 diagrams of the hypocotyl are at the left, those of the epicotyl 

 at the right. 



ULMACE.E. 



Ulmus americana. 



Structure of Hyfocotyl. 



The epidermis is composed of cells which, in cross section, 

 are square or rounded. After secondary growth of the stele has 

 commenced these cells become very much flattened. There is 

 no hypoderma differentiated. The cells of the cortex are large ; 

 all are about the same size. 



The endodermis is small-celled and is easily recognized in 

 early stages, when it contains very little starch. Afterward 

 starch becomes abundant in the endodermis, pericycle, cortex, 

 phloem and inner xylem. 



In the stele there are many small phloem bundles which are 

 confluent into two crescent-shaped areas. There are two xylem 

 bundles of somewhat crescentic appearance in cross section. 

 The xylem and phloem soon form closed rings. 



The pericycle, in seedlings which have about two internodes 



