864 



Transactions. 



/ dar-saJ^J 



Forking of Stele in a Young Plant 

 OF L. VOLUBILE. (Case 1.) 



f ct^r-scL^J 



Forking of Stele in Older Plant 

 OF L. VOLUBILE , Casc 2.) 



Series of sections at the point of branching were cut in a large number 

 of plants of various stages of growth, and the general result arrived at was 

 as follows : (1.) In young plants where the number of protoxylem groups 



in the stele is not more than five there 

 is no " parallel " rearrangement of the 

 bands preparatory to branching, but 

 the protoxylem groups increase in 

 number by splitting. In the case 

 figured the stem had foui- protoxylem 

 groups, and the resultant branches four 

 and three respectively. (2.) In plants 

 where the protoxylem groups number from six to nine there is very 

 frequently, though not always, a marked disposition of the bands more or 

 less parallel to one another, the plane 

 of this disposition always being at 

 right angles to the plane of division. 

 In some cases, quite irrespective of 

 branching, owing to the constantly 

 changing disposition of the bands of 

 tissue in between successive branch- 

 ings, the stele may, apparently by 

 accident, come to show^ quite a parallel arrangement, which, however, soon 

 becomes lost again. (3.) In still older plants, where the number of proto- 

 xylem groups is more than nine, a more or less parallel arrangement 'is 



generally to be found in between 

 the branchings. In the matui-e 

 plant, where the number of proto- 

 xylem groups is from ten to six- 

 teen, the parallel arrangement is 

 very marked (Plate XXXlII, fig. 3). 

 The arrangement of the bands on 

 the ventral side of the stele is 

 broken up by the giving-off of the 

 adventitious roots. 

 In L. scariosum, as in the case of L. volubile, considerable attention 

 was given to the study of the development of the parallel arrangement of 

 the stelar bands in the growing plant, and the same general conclusion 

 was arrived at — namely, that generally, though not always, the parallel 

 arrangement makes its first marked appearance in connection with the 

 branchings. 



Branching is frequent and always 

 in the plane of the ground, and as in 

 L. volubile the stelar plates are always 

 disposed at right angles to the plane 

 of division. 



In the smaller branches of both L. 

 volubile and L. scariosum the parallel 

 arrangement is found in the older 

 parts, but becomes lost as the stele 



decreases in size. In the ultimate branchlets of both species there is marked 

 heterophylly, and the larger leaves are borne laterally in the plane of the 

 ground. There is no correspondence between this pecuUar leaf-arrangement 

 and the stelar arrangement, the latter generally being tetrarch and radial ; 



Forking of Stele in Mature Plant 

 OF L. VOLUBILE. (Gase 3.) 



[ dor sa-l] 



Forking of Stele in Two Young 

 Plants of L. scariosum 



