THE ANATOMY OF THE STEM OF THE PAPAVERACE^E. 603 



pound bundles, while the remaining median bundle pursues an independent course 

 for some distance before fusing with the stem cylinder. 



The entry of the leaf-trace in Romneya trichocalyx is effected in a very simple 

 manner. The trace consists of five to seven strands ; the three central bundles 

 usually fuse to form one large median bundle. The vascular tissue of the axillary 

 branch distributes itself half on either side of the entering leaf-trace and gradually 

 loses its independence by lateral fusion, although the median bundle maintains its 

 identity for a considerable distance. The traces from the lower leaves do not, 

 however, enter entirely by one gap, although the median bundle, as in the case of the 

 upper leaves, remains distinct. 



In Corydalis racemosa the leaf-trace at the moment of insertion on the stem 

 consists of three strands, one large median and two smaller lateral. The bundles of 

 the axillary branch fuse laterally to form two vascular masses (fig. 39), between which 

 the median leaf-trace enters, while the two lateral leaf-trace bundles enter by smaller 

 gaps between adjacent stem bundles. The same method is adopted in C. glauca, but 

 in C. capnoides the three bundles enter together. The median cord divides into 

 three just before entry, all five bundles showing variations in degree of fusion 

 amongst each other and with the stem bundles. 



Anatomical Peculiarities in the Stem of the Papaverace^e. 



In the foregoing pages attention has been drawn to certain peculiar anatomical 

 conditions in the structure of the stem of the Papaveracese, of which the following 

 are the more noteworthy : — 



1. Secondary Thickening in the Stem Base of Papaver orientate. 



An extra cambium forms in the medulla, producing xylem outwards and phloem 

 inwards. This is the only case of abnormal secondary thickening that has been met 

 with in the order. The condition is in all respects comparable with that described 

 by Sanio (7) as occurring in the stem of Tecoma radicans, and indications of a 

 similar anatomical peculiarity appear in Rumex crispus. 



2. The Secondary Thickening in the Walls of the Xylem of 

 Romneya trichocalyx. 



The pitted vessels and tracheids possess a double spiral thickening such as Leger 

 found to occur in Dendromecon rigidum, Benth. 



3. The Occurrence of Concentric Vascular Bundles. 



Concentric vascular bundles occur in Papaver Rhoeas, P. sbmniferum, P. 

 Isevigatum, P. aljnnum, and Glaucium corniculatum. The phloem invariably 



