2 r6 Sargant and Arber.—The Comparative Morphology of 
indeed, may be said to be without vascular tissue even in this case. In the 
others, P and P' alike run upwards from the stalk of the cotyledon into 
the stele, diverging as they penetrate the axis in order to enter the stele at 
different points. 
In two seedlings the stele of the hypocotyl is cut transversely where 
P and P' enter it. In both cases the three plumular bundles correspond in 
position to the principal traces of the second leaf. The cotyledonary traces 
enter on either side of the midrib. Thus there are five traces at the top of 
the hypocotyl, but they cannot be followed downwards in any series of 
preparations which we possess, partly because the hypocotyl is always 
curved, and partly on account of the numerous root-insertions. 
The seedling structure of the Zingiberaceae. We have already compared 
the sheath of Elettaria with the coleoptile of Avena , and have constructed 
an imaginary form with a vascular skeleton intermediate between the two 
(Text-figs. 5-7, p. 166). The force of this comparison is much increased by 
the observations just recorded on five other genera of the Zingiberaceae. For 
characters common to several genera within a family, and—so far as we 
know—confined to that group, are probably ancient. The presumption is 
that they are inherited from a common ancestor. 
All six representatives of their genera have two distinct bundles in 
their cotyledon ; in four genera these bundles enter the upper sheath. 
Their course within it is alike in all four, and very characteristic. In other 
words the vascular skeleton of the sheath in Amomum , Renealmia , and 
Roscoea is almost identical with that of Elettaria , and is different from the 
skeletons of any other cotyledonary sheaths which we have examined. In 
Alpinia the upper bundle from the cotyledon sometimes enters the sheath, 
but only penetrates it for a very short distance before turning back. Even 
in this reduced form the same asymmetric type of skeleton can be recognized. 
In Brachychilum the short upper sheath contains no bundles. 
These genera have other anatomical characters in common. The first 
node is alike in all of them. The cotyledonary traces enter the stele of the 
axis from opposite sides, making an angle of at least 120° with each other. 
They take their place among the two or three plumular traces which are 
continued downwards. In all the species examined, except Roscoea 
purpurea , a common group of protoxylem is found in the centre of the 
hypocotyledonary stele, which recalls the common group formed by the 
junction of P, P and M in the mesocotylar stele of Coix. This afterwards 
breaks up into the groups px x and px 3 (p. 198). 
Cauline roots are given off freely in the neighbourhood of the first 
node, and sometimes lower down. The well-defined root-plates found in 
the hypocotyl of Elettaria (Text-fig. 30, VIII), Amomum , and Roscoea 
recall the root-plates in the mesocotyl of Avena and other Grasses. 
