734 Hens low .— The Origin of Monocotyledons from Dicotyledons , 
dons, chiefly aquatic plants, are mostly without cambium, so, on the other 
hand, traces of cambium are to be found in Grasses and Sedges. 
Mr. A. Chrysler thus writes: 1 ‘A well-marked, though generally 
short-lived cambium occurs in the bundles just above the node and near 
the base of the leaf-sheath in certain Grasses.’ This fact is considered by 
him to lend support to the view that * Monocotyledons have been derived 
from some group possessing a cambium, probably the Dicotyledons ’. 
‘ A cambium 2 is present also in the bundles at the nodes of Scirpus 
cyperinus and other species. These features indicate that the Cyperaceae 
is one of the most primitive groups of Monocotyledons. The view which 
derives this class from an essentially dicotyledonous ancestry receives 
further support.’ 
In my former paper 3 I drew attention to the series of concentric circles 
in Nelumbium , apparently indicating the first stage of their dislocation from 
a primitive and more compact zone of fibro-vascular bundles. Miss Sargant 
observes that the ‘ regular orientation—-xylem inwards, phloem outwards— 
suggests that the leaf-traces were formerly linked together by a cambium.’ 
Miss Sargant also observes: 4 ‘ Traces of a cambium in the vascular 
bundles of monocotyledonous seedlings have been recorded by several 
observers, as in Zea> Typha , Lilium> Dracaena , and in the hypocotyl of 
Yucca arborescens , &c.’ 
She quotes Professor Qudva as saying : ‘ The persistence of a cambium 
zone in the bundles of certain Monocotyledons shows that we may logically 
consider them as derived from the more primitive Dicotyledons, by means 
of the early disappearance of the cambium, and an increase in the number 
of traces from each leaf.’ 5 
In addition to the above, Mr. Chrysler observes that ‘ something similar 
occurs in the development of the central cylinder of Araceae and Liliaceae. 6 
The simple siphonostelic stage persists in Acorus for several internodes, and 
the stem looks much like that of a Dicotyledon ; higher up some segments 
of the stele become amphiasol (sic. amphivasa.1 ?), and this may be regarded 
as the first appearance of a monocotyledonous character.’ 
Again, in speaking of the central cylinder, he adds: c Medeola and 
Lilium show the effect of long internodes combined with extended gaps in 
breaking up the central cylinder into several strands arranged in the cir¬ 
cumference of the circle.’ 7 ‘ The plan of the young stele,’ continues 
Mr. Chrysler, ‘as, e.g., in Smilacina , bears a close resemblance to that of 
Dicotyledons, and differs from the older state of the latter only in the 
absence of cambium. These considerations lead to the conclusion that the 
1 Bot. Gaz., xli, p. n ff. (Jan. 1906). 
2 Rev. by A. B. Plowman, Ann. of Bot., xx, pp. 1-33, PI. I, II, 1906. 
8 loc. cit., p. 512. 4 Reconstruction, &c., p. 144. 6 op. cit., p. 145. 
0 Bot. Gaz., xxxviii, pp. 161-4. 7 ibid., p. 177. 
