THE ANATOMY OF THE STEM OF THE PAPAVERACE^E. 593 



tinguishable from the general cortex, although Leger describes its presence as a 

 constant character of this species. 



Papaver somniferum, L. — A transverse section shows numerous vascular bundles 

 arranged in concentric circles, giving the general appearance presented by a mono- 

 cotyledonous stem (fig. 13). The exodermisis distinct, the chlorophyll zone is five to 

 seven layers in thickness, the pericycle is less sclerotic than in P. Rhceas, and there 

 is a gradual transition both in the shape of the cells and in the intensity of sclerosis 

 from the pericycle to the medullary rays. A band of non-sclerotic cells intervenes 

 between the sclerotic pericycle and the hard bast in the fascicular regions, but the 

 hard bast is not well developed in this species. 



Papaver pilosum, Sibth. — The anatomy of the stem resembles very closely that 

 of P. Rhceas. Both exodermis and endodermis are well marked, the pericycle is 

 very sclerotic, and this character is maintained in the medullary rays. The peri- 

 cycle closely surrounds the hard bast, save where the latter abuts on the sieve-tube 

 region. The vascular bundles are more deeply seated than in any of the preceding 

 species. 



Papaver orientate, L. — The main axis of this species is perennial, and gives 

 off erect annual shoots. The arrangement of bundles is monocotyledonous in char- 

 acter, as in P. somniferum, the smaller outer bundles being more or less imbedded 

 in. a slightly sclerotic pericycle. The cortex is composed of several layers of cells, 

 the outer alone containing chlorophyll. There is no distinct exodermis, and the 

 peripheral bundles frequently consist of phloem and laticiferous tubes only. 



Papaver Iwvigatum, Bieb., resembles in anatomy P. Rhceas, and concentric 

 bundles also occur as in that species. 



Papaver glaucum, Boiss. — The anatomy resembles that of P. Isevigatum in all 

 essential points. 



Papaver lateritium, Koch, is similar to P. Rhceas, but the hard bast is only 

 feebly developed. 



Papaver nudicaule, L.— The main stem is extremely short, while the erect axes 

 are correspondingly elongated and well developed. No distinct exodermis is visible, 

 and the chlorophyll zone varies in thickness. There are three or more layers of 

 green cells about half way down the axis, but below and above this level these cells 

 decrease in number and finally disappear altogether. The pericycle is thick and 

 sclerotic, merging gradually into the non-sclerotic rays, but abutting directly on to 

 the hard bast in the fascicular regions. 



Papaver alpinum, L. — This species on the whole resembles P. nudicaule, but on 

 a reduced scale. The peduncles are sometimes fistular. By some authors P. alpinum 

 is regarded as synonymous with, or merely a variety of, P. nudicaule. 



Papaver rupifragum, Boiss. — The structure of the stem is in all respects 

 comparable with that of P. Rhceas. Here also there is a tendency towards the 

 formation of concentric bundles. 



