186 BOTANICAL GAZETTE [SEPTEMBER 
all the veins, the hadrome is frequently absent, except in the 
midrib. 
The green leaves are sheathing, and provided with a long, strongly 
compressed blade, the structure of which is very markedly isolateral. 
By examining the anatomical structure of the blade one gets the 
impression that the peculiar position of the leptome and hadrome in 
the veins is due to a concrescence of the two halves of the leaf-blade, 
resulting in a more or less complete suppression of the morphologically 
ventral face of the blade. 
However, the development of the ensiform leaf of Irideae, as de- 
scribed by GOEBEL,‘ teaches us something very different. According 
to this author the singular shape and structure of the blade is caused 
not by a concrescence of the wo halves of the blade, but by the 
peculiar growth of the leaf-primordium. The young leaf becomes 
laterally compressed at a very early stage of its development, and it 
so happens that its dorsal face shows this flattened growth much 
more than the ventral. The real growing-point soon ceases to be 
active, while a new point takes its place and this is located on the 
extreme back of the primordium, and somewhat lower than the 
original. The leaf thus shows two apices, and the secondary of 
these grows out into a long bladelike organ, which consequently has 
no ventral face, and in which the arrangement and structure of the 
veins must follow other laws than in a normally developed leaf-blade. 
The real apex of the leaf is thus to be found at the upper part . 
the open sheath, while the bladelike organ represents merely @ 
secondary growing-point, which has surpassed the primary one. 
In the species of the section Bermuprana the leaf-sheath is usually 
much shorter than the ensiform blade; in the section ECHTHRONEM* 
on the other hand, the sheath may be traced to very near the apex 
of the blade; and finally, in the section Errexiiema the blade is less 
compressed and often much shorter than the open, sheathing portion 
of the leaf. It is interesting to see that although the leaves ilk 
ensiform in all these species, the internal structure nevertheless 
exhibits two types so far as concerns the disposition of the mestome 
strands, which are in a single plane, as in BERMUDIANA, OF in th 
parallel planes, as in the two other sections. But otherwise the 
5 In ScHENK’s Handbuch der Botanik 219. Breslau. 1884. 
