Notes . 
486 
the result is the apparent mesarchy of the whole strand. In Fig. 1 the three bundles 
are quite distinct, the two small laterals lying one on each side of the main strand. 
At this point the bundles have just left the hypocotyl. As they pass together up the 
cotyledon, the xylem from the lateral bundles spreads round the protoxylem of the 
main bundle, until the whole has a mesarch structure as shown in Fig. 2. In Fig. 3 
the whole mass of centripetal wood has moved to one side ; its position now may be 
Fig. 1. Roscoea ptirpurea. Triple strand entering the cotyledon. C x = cotyledonary trace. 
Fig. 2. Brachychilum Horsfieldii. Vascular strand showing mesarch structure. px = proto¬ 
xylem ; c.w. — centripetal wood. 
Fig. 3. Roscoea purpurea. Strand becoming exarch again with centripetal wood moving to 
one side. 
Fig. 4. Fused cortical bundles, B, about to join second cotyledonary trace, c 2 . 
compared with that of the fused laterals in Fig. 4. Finally in the upper part of the 
cotyledon the whole strand becomes exarch again. 
Figs. 1, 3, and 4 are all taken from sections of seedlings of Roscoea purpurea , 
but in Fig. 2, a section cut from a seedling of Brachychilum has been substituted for 
the parallel case in Roscoea , as the mesarch structure was first observed in this set of 
sections and is very striking. In a neighbouring section a small amount of phloem¬ 
like tissue is to be observed accompanying the centripetal wood, and this is also the 
