F1BRO VASCULAR TISSUES: PHLOEM 113 



of a similar nature in the portion of the ray contained in the wood. 

 If we now turn our attention to the ray on the left, a somewhat 

 different situation is presented to the eye. Here the cells are 

 entirely without starch, although they still show protoplasm and a 

 nucleus. Internally they are in line with the marginal tracheids 

 of the ray in the wood, which have been described in an earlier 

 chapter. Obviously there are two categories of cells in the rays. 

 of the phloem in Pinus, just as has been shown to be the case 

 for the radial parenchyma of the xylem. It will now be con- 

 venient to consider the relations of the various elements of the 

 phloem to one another. In this connection we may first discuss 

 the sieve tubes. It will be noticed that there are certain dark lines 

 stained with iodine occurring in groups on the radial walls of the 

 sieve elements. These are the transverse sections of sieve pores. 

 Parenchymatous cells of the phloem have no intimate relation to 

 the tubes, as no pits facilitate interchanges between the two types 

 of elements. The same statement holds in regard to the cells of the 

 ray shown on the right side of the figure. On the left, however, the 

 elements of the ray are clearly related to the sieve tubes by means 

 of sieve plates, distinctly differentiated on the side of the sieve 

 tubes, but not well developed on the side of the ray. It is evident 

 that there is a specially intimate connection between certain ele- 

 ments of the ray, which are contrasted with the remaining constitu- 

 ents by the absence of starch, and the conductive elements of the 

 phloem or sieve tubes. 



If the organization or, more correctly, the disorganization of the 

 phloem is followed more externally, it will be observed in the illustra- 

 tion that the ray on the right continues to retain its protoplasmic 

 contents and its grains of starch, while that on the left has entirely 

 lost its living contents. A further feature of the phloem as repre- 

 sented in the external region of the figure is the distortion and final 

 collapse of the sieve tubes, preceded by the loss of the delicate pro- 

 toplasmic lining surrounding the inner walls of these elements. The 

 parenchymatous cells retain their integrity in the collapsed region of 

 the phloem, precisely as is the case with the ray indicated on the 

 right of the figure. Another feature of the disorganization of the 

 phloem is the appearance of large masses or plugs of material, 



