Eamaley: anatomy op onagraceae. 685 



easily distinguished from the fundamental tissue. There may- 

 or may not be parenchymatous cells between these phloem 

 groups and the primary wood. The thick walled bast cells 

 found by Weiss in the medullary phloem of Onagra biennis 

 were not seen. 



Intra-xylar phloem. — The intra- xylar phloem islands, as their 

 name indicates, appear in transverse section, as isolated groups 

 of phloem tissue. The cells of which they are composed have 

 thin cellulose walls which are usually somewhat crushed and 

 distorted. Some sections show these islands partly formed 

 with the wood beginning to close in around them. The sym- 

 metry of the wood cells for some little distance just outside of 

 one of these islands is in nearly every instance somewhat dis- 

 turbed. In cross sections of fresh material the sieve tubes are 

 distinctly seen. 



It is a matter in which there is room for doubt as to whether 

 or not all these islands contain, in reality, phloem tissue. In 

 the few longitudinal sections obtained, which showed these 

 groups at all well, the cells did not present the characteristics 

 of vascular tissue. They are irregularly cylindrical or roughly 

 bi-conical, not greatly elongated. As a rule the longitudinal 

 diameter is not more than two or three times as great as the 

 others. 



These islands are not present in very young parts of the 

 stem, nor do they occur in stems which attain only a slight 

 thickness. They usually appear in cross sections as patches 

 having a width of from three to eight cells in a radial direction 

 and extending, in the direction parallel to the circumference of 

 the section, from a distance of half a dozen cells to an eighth 

 or a sixth of a circle. Commonly they are so arranged that 

 they form more or less interrupted circles within the woody 

 zone. In sections of thick portions of the stem, these circles 

 are usually placed at about equal distances apart, and are read- 

 ily distinguished if the preparations be stained with some ap- 

 propriate mixture as fuchsin and methyl blue or iodine green. 



Phloem islands were found in the following plants: Anogra 

 pallida, Megapterium missouriensis, Oenothera rhombipetala, 

 Oe. sinuata and Onagra biennis. In the first named species 

 they are apparently not always present even in stems of some 

 thickness. In Megapterium missouriensis small patches of 

 phloem are to be seen in sections of stems which are 3mm. or 

 more in thickness. Much larger patches are found in Oeno- 

 thera rhombipetala. The islands in this species sometimes ex- 



