.] DEGENERACY OF THE STEM 99 



gravity, which builds up a stem really composed 

 of woody girders to meet the ever increasing 

 weight of the stem. Such is not necessary in 

 submerged or subterranean rhizomes, so degrada- 

 tion at once sets in. 



The order of retrogression may be speculatively 

 suggested to have been as follows : First, the 

 cords of the xylem-cylinder remain isolated, no 

 interfascicular cambium completing the zone ; 

 secondly, a second series of cords forming 

 another zone belonging to the next sheathing 

 leaf-base forms a second circle, then a third, 

 fourth or more would follow. The result would 

 be a series of concentric circles as are seen in 

 Nelumbium. The last and easy stage is reached, 

 when the internodes are arrested, and may, 

 perhaps, result from a simple dislocation of the 

 cords, so that the regular circles are broken up, 

 and the ordinary type of a monocotyledonous 

 stem results. 



If we compare the development of the leaves 

 of a member of the Nymphceacece with that, say, 

 of Sagittaria sagittcefolia, we see very remark- 

 able coincidencies. In a germinating plant of 

 Victoria regia (fig. 24) the first leaf is alto- 

 gether deprived of a limb, being reduced to a 

 petiole with a medial rib ; the second has a 

 lanceolate limb, the third a hastate, and the 

 fourth sagittate-peltate. The subsequent, perfect 

 floating leaves are orbicular-peltate. 



