the Embryo and Seedling in the Grammeae. 
217 
The upper sheath in the Zingiberaceae, when it contains any vascular 
tissue at all, is stiffened by one of the bundles which enter it from the stalk 
of the cotyledon. After running obliquely upwards, this bundle turns 
sharply down, and enters the axis from the base of the sheath. No part 
of such a bundle passes directly from stalk to axis. The second bundle 
may do so ( Roscoea. Alpinia ), or it may just enter the upper sheath on the 
side opposite the first bundle, and then turn downwards through the lower 
sheath to the axis ( Elettaria , Amomum , Renealmid). But all the bundles 
found in the upper sheath enter it from the stalk of the cotyledon, and 
leave it on their way to the hypocotyl. The same is true of Tigridia 
(Text-fig. 8, p. 168) and of Commelina coetestis , which we are about to describe. 
But this form of vascular skeleton is not universal in the upper sheath of 
Monocotyledons. We shall describe the seedling of 
Colchicum autumnale as an example of another type. 
Commelina coelestis , Willd. The lower sheath is 
long, and consists of the cylindrical base of the cotyledon 
enclosing the plumule. Above it is the upper sheath, 
which forms a hood and seems to have arisen from a sharp 
twist in the stalk of the cotyledon, just where it was 
spreading out into a simple sheathing base (Text-fig. 35). 
Two main bundles enter the sheath from the stalk, and 
behave very much like those of Elettaria. The upper 
bundle (P) travels nearly to the top of the hood before 
bending back to the axis, while the lower one (P') turns 
down almost as soon as it enters the sheath. 1 One or 
two additional bundles are sometimes found in sheath 
or stalk, but they are slender and end blindly, and are 
probably mere mechanical stiffenings, produced where they are needed. 
In Commelina the asymmetrical course of the two main bundles is 
probably due to the distortion of the originally simple sheath. After they 
have traversed the lower sheath, they approach the stele of the axis from 
opposite sides as in Elettaria. Two plumular traces are present at the first 
node, but there the resemblance ends. The plumular traces insert them¬ 
selves on P and P\ each of which becomes double. These double bundles 
face each other throughout the rather long hypocotyl, and ultimately form 
a tetrarch root. The anatomy of the hypocotyl is precisely that of some 
Dicotyledons, as for example Althea . 2 The details of transition to a root- 
structure are masked by the insertion of cauline roots. 
1 Attention has been drawn to the asymmetrical behaviour of the two bundles in the cotyledon 
sheath of another species of this genus by Martha H. Hollinshead : Notes on the Seedling of Com¬ 
melina communis, L. Contributions from the Botanical Laboratory of the University of Pennsylvania, 
vol. iii, No. 3, p. 275, 1911. 
8 Gerard, R.: Ann. des sci. nat., ser. vi, Bot., t. xi, PI. XVI, Fig. 23, 1881. 
Text-fig. 35. 
Commelina coelestis, 
Willd. Outline of 
sheath and adjacent 
parts; enlarged. 
