An Example of Leaf-enation in Allium ursinum L. 51 
mostly situated next the upper side, 
while the xylem is towards the sto- 
matal side (Menz, 1922, Text-fig. 2 b ). 
This condition has been brought 
about by torsion in the “petiole” 
and has been noted before by Goebel 
(1905, p. 296). Here the morpho¬ 
logically upper side has developed 
the structure of the morphologic¬ 
ally lower side. Keeping this fact 
in view it becomes clear that in the 
case of the abnormal leaf the ap¬ 
parently upper surface of the leaf is 
morphologically the lower surface. 
Thus the smaller blade has in rea lity 
been produced on the morphologic¬ 
ally upper surface of the leaf, but, 
most probably on account of torsion 
of the petiole below the point where 
it was broken off, it appears to be 
on the lower surface of the leaf. 
Not only has this abnormal leaf 
developed a second blade, but it 
has also formed a second “petiole” 
to support it (Fig. 1). This splitting- 
up of a “petiolar” region of a leaf 
seems to be unique. A large num¬ 
ber of examples of leaf-enations 
have been described, both from the 
upper and from the lower surface, 
in monocotyledons as well as in 
dicotyledons, but in no case is 
there any record of the enation ex¬ 
tending below the insertion of the 
“lamina.” Masters (1869), Worsdell 
(1915), Celakovsky (1884 and 1892), 
Velenosvky (1907, pp. 408-11) and 
Buchenau (1888 and 1891) have 
described and figured a number of 
leaf-enations, and I have examined 
all the examples of leaf-enations in 
Fig. 1. Allium ursinum. The abnor¬ 
mal leaf as seen from the lower sur¬ 
face. Portions of the lower blade are 
cut off to show the lateral “ribs” of 
the upper blade. c.r.„ central “rib”; 
l.r., lateral “ribs.” xf 
4—2 
