THE ANATOMY OF THE STEM OF THE PAPAVERACEvE. 591 



The laticiferous tissue, so characteristic of the Papaveracese, is found in the 

 phloem, and is arranged in an arc between the primary and secondary elements 

 (fig. 6). The tubes are articulate, and form a much-branched network (fig. 7). In 

 the developing stem protuberances arise from the vertical tubes, which push their 

 way between adjoining sieve tubes and unite with other later tubes in the vicinity. 

 The course of the tubes may readily be observed if fresh material be boiled for a few 

 seconds in a 10 per cent, solution of KOH and afterwards well washed and sectionised. 

 The xylem is separated from the medulla and medullary rays by conjunctive par- 

 enchyma, and similar cells are interspersed among the xylem elements themselves. 

 The protoxylem elements have single or double spirals followed by annular and later 

 by pitted vessels. The older secondary wood consists of radially arranged pitted 

 tracheae and fibres, the latter forming the main mass of the secondary tissue and 

 corresponding to the conjunctive parenchyma of the primary xylem (figs. 8, 9). 



The secondary phloem consists of narrow elongated elements with a few laticiferous 

 tubes. Only very rarely is anything in the nature of a sieve tube or companion cell 

 recognisable (fig. 4). The narrow elongated cells are, however, in protoplasmic 

 communication with each other through their lateral walls. The secondary latici- 

 ferous tissue is in the form of tubes running side by side and connected by large 

 perforations in contiguous walls. 



A transverse section through the basal region of the stem shows, as Leger points 

 out, marked differences from such a region as that already described. The epidermis 

 is deficient in cuticle ; the cortex consists of about seven layers of non-green, 

 slightly elongated cells ; the pericycle and hard bast are much less lignified, and 

 finally, in regions nearest the base, form with the cortex one homogeneous zone of 

 thin-walled cells. Meanwhile the vascular bundles coalesce and both secondary 

 xylem and phloem are produced abundantly. Medulla and medullary rays are 

 slightly lignified. The internodes are short, owing to the crowding of the radical 

 leaves, and the epidermis and outer layers of the cortex tend to die off and 

 exuviate. At the points of entry of an axillary shoot concentric bundles often 

 'appear, the occurrence of which is not noted by Leger (fig. 10, a). The phloem in 

 these cases is central, and has associated with it a complete ring of laticiferous vessels 

 (fig. ll). The secondary xylem in this region consists entirely of lignified fibres 

 with pitted walls. 



Leger describes the course of the vascular bundles only in the regions immedi- 

 ately below the flowers. The anatomy of several floral axes was investigated right 

 through the thalamus ; some of these flowers had eight, some ten, and others 

 thirteen carpels, but they all agreed in their essential characters, and the following 

 account may be taken to apply equally well to all types examined. The vascular 

 bundles of the pedicel are arranged in a ring, large and small bundles usually 

 alternating. These bundles, as the thalamus is approached, increase in number by 

 repeated divisions until an almost complete cylinder of vascular tissue has been 



