?,\4 



Transactions. 



In region 3 the fusion of bundles of the outer ring with medullary 

 bundles is traced; but the whole is gradually merged in the one ring typical 

 of the structure of the subsidiary roots in M. excelsum. 



Hypocotyl. 



The details of transition in the hypocotyl in M. excelsum. were not at 

 all rigid. There are six plumular traces, which are arranged on either 



Fig. 8 



Fig. q 



Fig. 7. Transverse cotyledon, M. excelsum, passing through midrib : a, upper ; b, lower 



epidermis ; c, xylem ; d, phloem. X 150. 

 Figs. 8 and 9. Hypocotyl below entry of cotyledon- traces. X 150. 



side of the axis in threes. These appear to fuse together, the xylems first 

 of all. A single cotyledonary trace enters from each cotyledon. On 

 its entry the phloem. is found in two masses on either side of the xylem ; 

 the elements travel towards the centre, 

 and leave the protoxylem exarch, as in 

 Peperomia amplexifolia, P. tithymaloides, 

 and P. maculosa. The phloem masses 

 ultimately fuse with the plumular phloem ; 

 as the xylem from the plumular traces 

 moves also towards the centre a central 

 plate of xylem is formed ; and we find a 

 typical diarch structure. But the plumu- 

 lar xylem may be very small in amount ; 

 so that, as in Piper cornifolium, the central 

 plate is composed mainly of elements 

 derived from the cotyledonary traces. 

 But in one seedling examined the plate 

 was composed mainly of elements derived 

 from the plumular traces, while the mes- 



arch elements from the cotyledonary traces decreased in amount. The 

 plumular traces showed lignified tissue, and were not wholly meristematic, 

 as in Piper cornifolium. 



Transverse petiole, young plant of 

 M. excelsum : b, dorsal ; a, ventral 

 side; c, bundle, x 44. 



Root— Macropiper excelsum. 



Ln M. excelsum the roots are adventitious. The primary root is very 

 early lost. On uprooting the plant one finds it characteristically forked. 

 Very often a seedliug bearing only the two cotyledons has lost its primary 

 root. 



