NOTES 
NOTE ON THE MESARCH STRUCTURE OF CERTAIN VASCULAR 
BUNDLES IN THE COTYLEDONS OF SOME SCITAMINEAE. —The presence 
of bundles possessing a distinctly mesarch structure was first observed in this Order 
by Miss Sargant, in transverse sections of the sucking cotyledon of Brachychilum 
Horsfieldii , and the occurrence of short, broad, spirally-thickened tracheides situated 
centripetally to the protoxylem was at once confirmed by longitudinal sections 
of the seed and enclosed cotyledon. 
The question arose as to whether this was a primitive character, or whether the 
presence of this centripetal xylem could be otherwise accounted for. The fact that 
the bundle was exarch in structure before it entered the cotyledon, then became 
mesarch for a space, but again became exarch towards the tip of that organ, seemed 
to indicate that this variation in structure might be due to some local adaptation. 
Besides Brachychilum , the cotyledons of the Scitaminaceous seedlings, Alpinia 
calcarata , Roscoea purpurea , and Elettaria Cardamomum, were examined ; those 
of Alpinia and Roscoea were found to resemble that of Brachychilum closely, not 
only in the presence of an apparently mesarch bundle, but in other features. In 
Eleltaria , however, no such mesarch structure was found. 
In the three former species the haustorial part of the cotyledon is provided with 
two vascular bundles; one of these passes into it directly from the stele, the other 
travels through the cotyledonary sheath first. Definite mesarch structure is only 
present in that which comes direct from the stele, but the relations of the constituent 
bundles of the two strands within the sucking cotyledon can be more easily traced in 
the other, and thus an explanation of the mesarch appearance of its companion 
arrived at. 
When this trace is on the point of leaving the cortex and entering the cotyle¬ 
donary sheath, it is joined by two small lateral bundles which form part of a cortical 
anastomosing system connecting the traces of all the leaves together. Sometimes 
these two small bundles fuse and join the main strand as one bundle, sometimes there 
is a short connecting branch between them, but in either case we have as a result 
a small bundle running close past the protoxylem of the main strand. Thus in 
Fig. 4 the smaller bundle, b, is formed by the union of the two laterals which have 
taken the courses indicated by the dotted lines, and it will be seen that one has passed 
very close to the protoxylem of the main cotyledonary strand, c 2 . 
In the second cotyledonary strand which passes direct from the stele to the 
sucking cotyledon, this crossing of the paths of the three constituent bundles takes 
place while the two small cortical bundles are associated with the main trace, and 
[Annals of Botany, Vol. XXIV. No. XC 1 V. April, 1910.] 
