88 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN [VOL. 10 



the sclerenchyma ring are not completely ensheathed by selerenchyma, but have 

 a few such cells at their phloem poles. A single layer of thick-walled sclereids 

 forms the outer layer of the ring. Internal to this layer are several layers of 

 lignified parenchyma cells. Just interior to these cells, in the periphery of the 

 central zone of the central zone of thin-walled parenchyma, is a single ring 

 of about 5 bundles. 



4. A. ciliata (fig. 50). At the level shown, the inflorescence axis is surrounded 

 by a bract. This may account for the occurrence of lignified papillate epidermal 

 cells. The cortical zone consists of spherical chlorenchyma cells. A number of 

 bundles, each surrounded by an arc of sclereids, is present outside the scle- 

 renchyma ring. The inner portion of the ring intergrades with the thin-walled 

 parenchyma in the ''pith" region. Within this latter zone, several (about 6) 

 bundles occur. These bundles are notable for the occurrence of a prominent 

 protoxylem lacuna which is separated from the remainder of each bundle. An 

 additional set of bundles is interposed between those just mentioned and the 

 inner margin of the sclerenchyma ring at lower levels in the inflorescence axis, 

 and presumably these bundles supply a bract, and are thus absent at the level 

 shown. 



5. A. linearifolia (fig. 51). Although inflorescence stems in this species are 

 larger in diameter than the above, they are not markedly different in most 

 respects. One notable feature is the occurrence of a single hypodermis layer. At 

 levels lower than that shown, two layers were apparent. A feature not previously 

 indicated is the presence of bundles (in addition to those at the outer margins 

 of the sclerenchyma ring) within the ring itself. Additional bundles are present 

 in the "pith" region. At lower levels, all bundles (except those at the outer mar- 

 gin of the ring) are located in the thin- walled portion of the central ground 

 tissue. 



6. A. macrostachya var. angustior. Upper levels in the inflorescence axis 

 of this variety show a structure like that mentioned for such levels in A. 

 linearifolia, except that the cortical region consists wholly of parenchyma cells 

 like those of the hypodermis. At lower levels, however, 2-3 hypodermis layers 

 are present; interior to these is chlorenchyma. Outside of the sclerenchyma 

 ring, numerous bundles occur; these are embedded in the non-photosynthetic 

 parenchymal single layer of strongly thickened sclereids forms the outermost 

 layer of the sclerenchyma ring, and several layers of lignified parenchyma occur 

 within that layer, as described for A. americana. Numerous bundles are present 

 in the central thin-walled ground tissue. The tendency toward amphivasal con- 

 struction of bundles is prominent at lower levels. 



7. A. macrostachya var. macrostachya (fig. 53). In the section shown, the 

 cortical tissue consists of non-photosynthetic parenchyma. At higher levels, 

 chlorenchyma is present interior to one or two layers of hypodermis. In addition 

 to the bundles at the outer margin of the sclerenchyma ring, there are a few 

 embedded in its inner margin (fig. 53). Many bundles occur in the thin-walled 

 central ground tissue. Each of these bundles possesses a few lignified elements 

 near the phloem pole. Such elements are absent at lower levels. 



8. A. macrostachya var. robustior (fig. 54). This inflorescence axis is quite 

 similar to that of the above variety, but several features are worthy of note. 

 The bundles at the exterior of the sclerenchyma ring are much smaller than 



