FJ., 1921] HARRIS AND OTHERS SEEDLINGS OF PHASEOLUS 67 



fo th the protoxylem in an endarch position, begins to be assumed. Each 

 pir is subsequently referred to as a &quot;primary double bundle.&quot; Thus the 

 li/el of transition from root structure to stem structure is low, being prac- 



FIG. I. Dimerous seedling. Transverse section through the root, showing its 

 trarch condition (four protoxylem poles). FIG. 2. Dimerous seedling. Transverse 

 s:tion through the base of the hypocotyl showing the four primary double bundles, each 

 c which has been derived from one of the four root strands. FIG. 3. Dimerous seedling, 

 &quot;ansverse section through the mid-region of the hypocotyl showing the normal eight- 

 tndled condition. No intercalary bundles are figured. FIG. 4. Dimerous seedling. 

 1 ansverse section just below the cotyledonary node. The four bundles or bundle groups 

 tve originated by a more or less complete fusion of the adjacent members of each of the 

 ciginal pairs. Each bundle, as shown by the two constrictions in it, is about to break up 

 i;o the three strands shown in figure 5. FIG. 5. Dimerous seedling. Transverse section 

 trough the cotyledonary node. Each group of three strands which have arisen by a 

 leaking up of the large bundles in figure 4 is here enclosed by a dotted line. These three 

 e ands are a cotyledonary trace (solid black), an epicotyledonary bundle, and a small 

 hndle which will fuse with its adjacent neighbor to form another epicotyledonary bundle. 

 ?;G. 6. Dimerous seedling. Transverse section through the mid-region of the epicotyl 

 sowing the twelve bundles which have arisen by the splitting of the six original epicoty- 

 llonary bundles. The six strands which are to go off as traces to the two primordial 

 lives are solid black. 



cally at the base of the hypocotyl. The members of each of these four 

 ]iirs soon separate until the eight bundles are approximately equidistant 

 ig. 3), a condition which persists throughout the hypocotyl until the coty- 

 donary node is approached. 



In addition to these bundles, there are in a considerable percentage of 

 le normal seedlings studied a variable number of accessory or intercalary 

 undies, the &quot;Zwischenstrange&quot; of Dodel. These may make their appear- 



