On the Structure of the Androecium in Parnassia 
and its bearing on the Affinities of the Genus, 
BY 
AGNES ARBER, D.Sc., F.L.S. 
Fellow of Newn ham College , Cambridge. 
With Plate XXXVI and four Figures in the Text, 
Contents* 
PAGE 
I. Introduction •••••••*•* 49* 
II. The Anatomy of the Androecium in Parnassia . 49 2 
(i) The Anatomical Relation of the Androecium to the other Whorls of the 
Flower in Parnassia palustris , 49 2 
(ii) The Anatomy of the Stamens in Parnassia palustris , L., and other species . 494 
(iii) The Anatomy of the Nectaries in Parnassia palustris , L. . 497 
III. A Suggested Interpretation of the Mesarch Structure in the Stamen-filaments of Parnassia 497 
IV. Discussion of the Affinities of Parnassia . ..... 500 
V. Summary 509 
Explanation of Plate XXXVI . . 510 
I. Introduction. 
F IVE years ago, in the course of an examination of the anatomy of the 
stamens of various Dicotyledons, I cut some serial sections of flowers 
of Parnassia palustris , L., which had been collected in Middleton Dale, 
Derbyshire. I was immediately struck by a curious feature in the anatomy 
of the filament, namely, the occurrence of centripetal xylem in connexion 
with the single xylem strand which traverses it. At the time I was unable 
to arrive at any explanation of this peculiarity, so I laid the subject aside. 
More recently, however, a possible interpretation of this structure has sug- 
gested itself to me, and, since this interpretation appears to have some 
bearing on the vexed question of the systematic position of the genus 
Parnassia , I have thought it worth while to describe my observations in 
the present paper, and to discuss certain theoretical views connected with 
them. 
I have much pleasure in expressing my gratitude to Mrs. Henshaw for 
her great kindness in collecting, on my behalf, a large number of specimens 
of three species of Parnassia in the Canadian Rocky Mountains. 
[Annals of Botany, Vol. XXVII. No. CVII. July, 1913 .] 
