252 Arber. — Studies on Intrafascicular 
metaxylem, consisting of elements of large lumen, and (iii) smaller elements, 
which I interpret as arising secondarily from the intrafascicular cambium. 
I have since noticed this differentiation in two additional cases — Leucojum 
aestivum , L. (Amaryllidaceae) and Gladiolus sp. (Iridaceae). In the paper 
in question I also described and figured certain instances in which the 
xylem of a lateral branch of a foliar bundle owed its origin exclusively 
to the secondary xylem of the parent bundle. Recently I have seen a case 
of this in three other plants — Crocus carpetanus , Boiss. et Reut. (Iridaceae), 
Asphodelus liburnicus , Scop. (Liliaceae), and Aneilema giganteum , R. Br. 
(Commelinaceae). 
Among the Palms, only two cases of intrafascicular cambium have 
been hitherto recorded ; 1 to these I can now add three further examples. 
In serial sections of the shoot apex of Rhapis humilis , Blume, the bundles, 
both in the young leaves and axis, show cambial activity (Fig. 1), and 
I have also seen the same thing in the plumular leaves of Chamaerops 
humilis , L., and Areca sapida , Soland. 
In the case of the Araceae I recorded in 1918 2 the occurrence of intra- 
fascicular cambium in the rhizome of Acorus Calamus , L., and I have since 
found this tissue in the very young petiole of Calla palusfris, L. (Fig. 2). 
In 1914 Lignier 3 described and figured cambium in the petiolar bundle of 
Aru 7 n maculatum , L., stating, however, that he had examined the mature organ j 
only. His account is somewhat intriguing, since, although he describes the 
cambium as giving rise to phloem alone, his figure shows a differentiation 
of the wood into protoxylem, then large-lumened metaxylem, and then 
xylem elements of smaller calibre, which he also regards as part of the 
primary wood. I should myself have supposed these latter elements to 
be secondary, since they recall in arrangement and appearance those 
small xylem elements which I have shown to be of cambial origin in 
the leaves of Anigozanthos , &c., 4 and to which I have again referred in 
an earlier paragraph of the present paper. In order to try and get fur- 
ther light on the nature of these elements in Arum , I have studied 
microtome sections of apical buds, and hand sections of older leaves of 
Arum italicum , Mill., a species closely related to A. maculatum . These 
sections show that, in the bundles of the petiole and midrib of the very 
young leaf, there is a radial seriation involving most of the elements between 
the protoxylem and protophloem. This stage is seen in Fig. 3 A, which was 
drawn from a leaf so young that the petiole was only about 0-7 mm. 
in diameter. In the bundles of the midrib and petiole of the mature leaf 
(Fig. 3 B) the protoxylem is followed by a few large elements (m.x.), which 
I take to be primary metaxylem ; to these again succeed a number of small 
elements (#. 2 ), whose seriation in radial files, which continue into the 
1 For references see Arber, A. (1917). 
3 Lignier, O. (1914). 
2 Arber, A. (1918). 
4 Arber, A. (1919). 
