S4 BULLETIlSr 365, U. S. DEPARTMENT OF AGRICULTURE. 



Group 6 is represented by Delphinium ajacis (PL VI, fig. 2, and 

 fig. 4, A and B). Tlie stem is circular and lias a relatively small 

 medullary lacuna. The bundles are about 46 in number and are of 

 two sizes, the large and small arranged alternately. This is the only 

 group in which it w^as possible to distinguish a row of endoclermal 

 cells. All the cell walls are much thickened, which is a distinguish- 

 ing characteristic of this group. The shape of the fibrovascular 

 bundles is quite characteristic. The bast is w^edge-shaped, composed 

 of cells whose walls are so thickened that the lumen is reduced almost 

 to a point. The phloem is small and completely inclosed hy the 

 bast and xjdem. The xylem mass is larger than the bast, elongated, 

 and includes a large amount of xylem parenchyma. 



Delphinium consoUda is similar to D. ajacis, but the bundles are 

 less numerous, the cell walls in the pericycle are thickened still 

 further, and part of the cells of the cortical parenchyma have thick- 

 ened walls. 



Any of the species which were examined could be quite easily 

 placed in one of the above groups, but within the groups the work 

 thus far done has not revealed sufficiently characteristic differences 

 in stem structure to make identification of species possible. Vesque, 

 1881, page 29, says that while it is impossible to distingaiish genera 

 by anatomical characters, it is eas}'' to distinguish species, but he 

 uses different characters to differentiate the species, such as the struc- 

 ture of the petiole, the development of palisade cells, and the dis- 

 tribution of stomata in the leaf. On the other hand, the present 

 work is based on stem characters, which serve to differentiate be- 

 tween genera in the family Eanunculaceae, and in this case between 

 groups of species in the genus, but not between individual species. 

 An exception to this is group 6, of which we have only two species 

 in America, and these two can be distinguished by the anatomy of 

 the stem. These two are European species which have been intro- 

 duced into the United States, and are described anatomically by 

 Lenfant (1897, pp. 26-27, PL VII) and Marie (1885, pp. 117-118, 

 PL VI). The specimens of ajacis and consolida from the Na- 

 tional Herbarium which were examined had evidentl}^ been mis- 

 named, one for the other, as was discovered by comparing cross sec- 

 tions of the stems with the descriptions and figures of Marie and 

 Lenfant. 



Sections were also made of two species of Aconitum, A. hakeri 

 Greene (PL VI, fig. 3; and fig. 5, A and 5) and an unidentified species 

 from California, in order to compare them with and to differentiate 

 them from the tall larkspurs. The cross section of the stem shows a 

 structure similar to that of the tall larkspurs, but it can be easily 

 distinguished by the lack of a medullary lacuna, and by the complete 



