i6o 
Note . 
position. In herbarium material, the phloem cannot be recognized with certainty. 
As regards the xylem, the bundle closely recalls certain forms assumed by the 
vascular structures in the filament of P. palustris , as may be seen by comparing 
the figure of the present note with PI. XXXVI, Fig. i of my previous paper. 
(In both these figures the adaxial side of the stamen lies to the right of the diagram.) 
In the next species, P. Wightiana , the bundle is small, and, though the xylem 
opens out in the connective, no other sign of complexity can be detected, except that 
there are occasional indications of a centrally-placed protoxylem in the filament. 
This Indian species has thus reached a stage of reduction in the stamen-anatomy 
comparable with that obtaining in the American form P. montanensis. 
In Parnassia ovata and the minute species P. pusilla , the bundle is very small. 
I have found no trace here of the anatomical complexity 
in the filament, which seems to be confined to the larger 
members of the genus with stouter stamens. These 
two species may thus be compared with the American 
form P.parviflora , whose slender filaments are traversed 
by a simple bundle. It may be recalled that Hooker 
and Thomson 1 have suggested that P. pusilla and 
P. ovata may perhaps prove to be merely forms of 
P. nubicola. If this were so, it would confirm the 
view that their stamen-anatomy represents a stage in 
reduction from the more complex type found in 
P. palustris , P. fimbriata , and P. nubicola. 
Since the presence of additional xylem elements 
on the adaxial side of the filament bundle has now 
been recorded in three species belonging to two dif¬ 
ferent Sections of the genus Parnassia , and natives, 
respectively, of Europe, America, and Asia, and since, 
in the only cases so far examined in which this com¬ 
plexity is absent, the bundle may reasonably be re¬ 
garded as having undergone reduction, we may infer 
that the structure in question Was probably character¬ 
istic of the common progenitor of the genus. As I have previously suggested, the 
unique features observed in the anatomy of the androecium may be interpreted as 
indicating that the single stamen of Parnassia has been derived by reduction from an 
ancestral stamen-fascicle. 
AGNES ARBER. 
Balfour Laboratory, Cambridge, 
June 5, 1914. 
Parnassia nubicola , Wall. 
Transverse section of xylem 
group in filament a short dis¬ 
tance below insertion of anther. 
The adaxial surface of the sta¬ 
men would lie to the right of 
the diagram, cfx. = centrifugal 
xylem ; px. = protoxylem ; cpx. 
= centripetal xylem. ( x 636.) 
1 Hooker, J. D., and Thomson, T. : Praecursores ad Floram Indicam. Journ. of Proc. Linn. 
Soc. Bot., vol. ii, 1858, p. 78. 
