THE ANATOMY OF THE STEM OF THE PAPA YEBACEJE. 595 



bast, and the outer portions of the medullary rays, the whole forming a continuous 

 cylinder of mechanical tissue. In section the laticiferous tubes which occur at the 

 periphery of the hard bast assist in differentiating pericyle from hard bast owing 

 to their larger lumina. Prantl and KtiNDiG state (I.e.) that in Glaucium laticiferous 

 tubes occur only in the roots, but this is not the case, and no doubt these authors 

 failed to recognise them in this situation. A few isolated tubes are also to be found 

 in the pericycle and medullary rays and in the secondary phloem. When old the 

 latex tubes lose their contents, and those external to the vascular bundles become 

 sclerotic. The cells are usually isolated, and show no tendency to form a series. 

 Although, as above stated, there is usually a gradual transition in the interfascicular 

 region from well-lignified pericycle cells to less sclerotic and finally non-sclerotic 

 medullary ray cells, sometimes the whole of the medullary ray as well as the 

 medulla itself is transformed into mechanical tissue. The xylem and phloem do 

 not call for remark beyond the fact that the sieve tubes are especially well 

 developed. 



Bocconia microcarpa, Max. — A transverse section through the stem of this 

 species shows a well-marked epidermis of brick-shaped cells whose walls tend to 

 become lignified (fig. 17). Beneath the epidermis lie a double layer of collenchyma 

 and two or three layers of chlorophyll-bearing cells. The collenchymatous cells 

 show traces of chloroplasts, indicating their modification from ordinary cortical 

 cells. Further, traces of collenchymatous thickening appear in the thin- walled, 

 green cortical cells, so that the difference between these two zones is one of degree 

 rather than of kind. No definite endodermis is discernible. The pericycle is only 

 slightly sclerotic, and in the interfascicular regions merges gradually into the 

 medullary ray tissue, which, like that of the medulla, is parenchymatous. The 

 vascular bundles are arranged in a single compact circle close to the periphery. 

 The xylem consists of vessels with bordered pits (fig. 18) and wood parenchyma. 

 Laticiferous tubes are found at the periphery of the hard bast, but in the adult they 

 become less obvious owing to lignification. They occur also on the inner margin of 

 the internal parenchymatous mass, and may be recognised, even when lignified, by 

 their large lumina and contents. 



Eschscholzia californica, Cham. — The stem of this plant is furrowed, the angles 

 being rounded and about ten in number, though varying in different regions of the 

 stem (fig. 19). Stomata occur in the furrows, while the subepidermal tissue opposite 

 the ridges is collenchymatous (fig. 20). The chlorophylliferous tissue lies in the 

 furrows, and merges into thin-walled parenchyma continuous beneath the collenchy- 

 matous bands. Many of the cells show traces of latex, but the latex tends to 

 disappear almost entirely in the adult, affording an explanation of the statement by 

 Prantl and Kundig (I.e.) that latex does not occur in the stem of this genus. The 

 pericycle is only feebly sclerotic, and is from one to three cells deep. The latex 

 tubes occur chiefly in the deeper cortex, though occasionally also in the secondary 



