the lips should be used as the basis for the separation of 
the two species. He stated that the lip was dorsi-ven- 
trally compressed in C.parviflorum and laterally com¬ 
pressed in C.pubescens. 
From the above remarks, one might surmise that both 
Willdenow and Hooker, as well as Salisbury, had a limit¬ 
ed amount of material from which to draw their conclu¬ 
sions. Indeed, it is very possible that each of these men 
had in hand a different form of the North American 
plant. 
In attempting to segregate a large number of herbar¬ 
ium specimens of our yellow Cypripediums into their 
respective specific or varietal categories, I have been 
completely baffled. It seemed, therefore, advisable to 
review all available literature on the subject in an effort 
to solve the problem. In doing so, I have been impressed 
by the comparatively few efforts which have been made 
to solve this puzzling problem. Although many authors 
have ventured opinions of doubt concerning the specific 
rank of C. parvijlorum and C. pubescens , most of them 
have blindly adopted the European concepts of our 
plants. In the following pages I have recorded some few 
of the opinions which have been broached by various 
writers from time to time. I have also proposed a new 
status for our North American yellow Cypripediums.* 
In trying to separate C. flavescens from C. Calceolus , 
de Candolle (Redoute Les Liliacees (1802) t. 20) said 
that the yellow-flowered slipper was a great deal like the 
slipper of the Alps (C. Calceolus) and that one would 
take it at first sight for a simple variety of this plant 
He ended by separating the two plants on the basis of 
coloration of the flowers, on the shape of the staminodes, 
and on their geographical distribution. 
paper is concerned only with those species found north of Mexico. 
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