2 I 8 
Eames. — On the Origin of the 
different anatomical structure, and serve to show transitional stages between 
the two extreme types. 
Sanguisorba canadensis , L., illustrates several points very well. The 
woody cylinder of the rootstock consists of a series of bundles, very unequal 
in size, and somewhat irregular in shape, all connected by a strongly marked 
interfascicular cambium. Many of these bundles, however, are much modi- 
fied ; their cambium has ceased to form xylem at various stages and with 
much irregularity, and has laid down parenchyma thereafter instead. 
Fig. 2 illustrates this condition. In some of them, after the formation 
of primary wood is completed, parenchyma replaces the secondary xylem 
entirely, or with the exception of a very few scattered vessels or fibres. In 
the aerial stem the bundles are reduced in size, and the stem resembles the 
herbaceous type more closely. At the base the connecting interfascicular 
cambium is clear ; in higher parts of the stem it gradually dies out. 
Fig. 3 shows a stage where only slight evidences of its activities are 
found ; and in the upper portions of the aerial axis there is no trace of 
cambial activity between the bundles. (The plants studied were of mature 
growth.) 
The genus Genm shows, in the few species examined, an interesting 
series in the aerial stems from forms with solid, though thin, woody cylin- 
ders to those possessing an herbaceous type of organization. The rhizomes 
of all species of Genm are similar to the underground stem of Sanguisorba. 
G. virginianum , L., the most woody of the species studied, has, throughout 
the most of its upright stem, a cylinder that is unbroken, save, of course, by 
brief leaf-gaps ; but at the top there is a partial separation of the woody 
cylinder into fascicular segments. The upper portions of the stem of 
G. canadense , Jacq., have small, widely separated bundles, quite typically 
herbaceous, although the rest of the stem is structurally like that of G. vir- 
ginianum. G. triflorum , Pursh, and G. rivale , L., have the aerial stem, with 
the exception of a very short piece at the base, dissected into separate 
bundles. This condition will be further discussed below. 
The chief interest in the genus Agrimonia lies in the ray development. 
The structure of the central cylinder of the rhizome and aerial stem of the 
three species which were examined, A. striata , Michx., A. gryposepala , Wallr., 
and A. mollis , Britton, is not very different from that of Genm virginianum . 
The rays of the rootstock consist of ray cells, typical in size, shape, and 
position. Conditions in the aerial stem are very different however. A 
cross-section of such a stem of A. striata shows numerous, well-marked 
uniseriate rays. But in the tangential section no rays seem to exist. 
That which resembles ray tissue in transverse section appears in this section 
as wood parenchyma. Rows of parenchyma cells, narrow and much 
elongated vertically, extend for long distances in the stem — through one 
internode at least. The radial section shows, however, that these long rows 
