84 JOURNAL OF THE [Jul.Vr 



Schultze's solution, losing its orange color and disappearing as 

 an amber fluid. It is not improbable that this gum has the medi- 

 cinal properties of gamboge, as Ottow found a poisonous glucoside 

 in the bark of the Wistaria. Mention is not made of the pro- 

 perties of this poison, and it may have no connection with tVe 

 resin, which does not occur in the bark. The latter term, how- 

 ever, may have been loosely used to include the inner cortex. 

 The origin of these cells is lysigenetic. In the young bast and 

 pith single cells of parenchyma are found filled with the resin; 

 but with growth, either through rupture or dissolution of contig- 

 uous walls, the resin spreads, forming irregular branching pas- 

 sages. In the pith the resin slowly disappears before the period 

 of degradation begins, but remains a constant feature of the 

 phloem. The dilatation of the bast becomes very noticeable 

 with the advance of age, forming the triangular white spots of 

 the cortex (Fig. 17). This enlargement is brought about largely 

 by the medullary rays, and usually by the multi-seriate ones. 

 These broaden as they are pushed out by the successive annual 

 zones, and by radial bipartition of the individual cells the 

 original size of the cell is approximately maintained. These 

 huge wedge-shaped masses of parenchyma often constitute the 

 larger part of the bast, and so intermingle with the parenchyma 

 of the outer cortical zone as to leave no line of demarkation be- 

 tween them. 



Considering now the periblem, it is seen to consist entirely of 

 parenchyma. The cells are filled with plastids containing chloro- 

 phyll, protein matter, and starch granules. These plastids are 

 circular or lenticular in form, often showing starch embedding in 

 or adhering to their surfaces. Fig. iS illustrates the forms of 

 plastids and starch granules found in the plant. The first 

 change in this external cortical zone is the formation of the phel- 

 logenetic meristem. This takes place in the external layer of 

 cells during the first year (Fig. 19). The development at 

 first is entirely centripetal. Of the two cells formed by the first 

 division, the outer one eventually becomes cork, while the inner 

 one continues to grow and again divides, the inner one ever re- 

 maining active. But after the fourth or fifth year the develop- 

 ment changes and becomes reciprocal. Now the inner of the 

 cells formed by the division of th-e mother cell is no longer 



