1 76 MEMOIRS FROM THE DEPARTMENT OF BOTANY OF COLUMBIA COLLEGE. 



(inwii. After passing a somewhat different epidermis and hypoderma, we meet with 

 quite similar starch-rings and stereome cyhnders, the latter being very compact and 

 rigid, the elements small, angular, and of much the same size throughout ; again passing 

 a difference in the arrangement of the phloem, the xylem appears strikingly similar in 

 both, with its system of tracheides and vessels disposed in the same manner ; the xylem 

 merges into the pith through a cylinder of the same kind of cells, and in both species the 

 latter tissue appears about the same in cross section, its difference in long section being 

 mentioned under the head of the subgenus To vara. 



Third : This division will include the subgenera Avicularia and Dura via. These 

 two are not thrown together on account of the similarity of their respective tissues, but 

 on account of the stereome development in the primary cortex. The phloem is peculiar 

 in each case, while in Avicularia the xylem is normal, but in Dura via it is not what 

 we should expect to find. 



Fourth: P. scandens falls in here with its large-celled epidermis, its often scanty 

 hypoderma and starch-ring, a characteristic stereome cylinder, its non-radial fascicles of 

 phloem and weak form of xylem with few tracheides and vessels. The inner sides of the 

 bundles also are strongly wedge-shaped. 



Fifth : This, the last division, embraces subgenus Echinocaulon. P. arifolium as 

 representive, shows a double epidermis, the only one found in this study, a very irregular 

 primary cortex, a strong and characteristic stereome cylinder, a scanty supply of phloem 

 and a remarkably strong and diversified system of woody fibres, together with numerous 

 and conspicuously marked tracheides and vessels. The pith elements in this case are 

 unusually large. 



After arranging and grouping the subgenera in a natural sequence based on their 

 anatomy, reference to pages 18 and 19 will show that this classification corresponds ex- 

 actly to the sequence and grouping there based on their morphology. 



Although the eight subgenera group themselves into five divisions as arranged 

 aljove, there is more or less dissimilarity among some of the tissues of those falling into 

 the same divisions. These variations suggest a number of interesting points. 



First : There is a difference in the development of the tissues! I have discussed this 

 with special reference to the classification and will attempt to give reasons for these differ- 

 ences. The general similarity of the tissues of each subgenus has been given above, and 

 this serves to show the distinction between the divisions, but a glance at the plates, 

 especially the cross sections, will show that more or less difference exists between the 

 members of the same division. 



Second: Are there any tissues wanting? I have stated that the same tissues are 



