POTAMOGETONS IN RELATION TO POND CULTURE. 271 



origin of tube-bearing structures, one arising near the base of the peduncle, the other 

 solitary from the axil of a leaf. Figure 44, A, is a detail of such a spray showing the 

 usual character of the runner. Runners arise also on the lower parts of the stem 

 (Irmisch, 1858). These, like many on the tips of the spray, may develop so late in the 

 autumn that tubers never mature. What their fate is during the winter can only be 

 conjectured. It is a fact, however, that when placed in aquaria they continue to grow 

 slowly and eventually produce small tubers, or remain for a time in a quiescent state 

 and then send forth leaves and other runners. 



In the gigantic form of pcctinaius (Dudley, 1886) the tubers are elongate and large 

 in size. They are born on runners at the bases of the stems just above the substratum 

 of mud, and are therefore several feet beneath the surface of the water. Figure 61 

 shows the entire leafy axis with a tuberous runner attached at the base of the stem. 

 This is the normal position for what appears to be the chief propagative structure of 

 this form of pectinatus, and the usual condition at the approach of winter. The runner 

 is seen in detail in figure 50. The tubers are yellowish in color, and when stripped of 

 scales, which envelop them at this season, appear as in figure 51. The remainder of 

 the runner is dark green in color, more or less contorted and tuberous, and hardened 

 throughout by storage of starch (fig. 50, B). Secondary runners bearing tubers (fig. 50, 

 I, 2) are additional features in what withal is a remarkable propagative structure. 

 Peculiar tuberous internodes, transition stages, perhaps, in the formation of tubers, 

 appear frequently and characterize the more hardened and resistant portions exclusive 

 of the terminal tubers (fig. 52). On germination a leafy shoot and runner are pro- 

 duced. Figure 55, an illustration of a similar feature repeated in a series, was devel- 

 oped in an aquarium from the terminal tuber of a small runner. It illustrates how 

 resourceful in the propagation of this species so small a structure may become. 



Young, green, leafy shoots arise from the fertile nodes of the runner (fig. 50, D) 

 and doubtless function in perfecting the propagative structures of this persistent part 

 of the plant, for at this time — that is, in the autumn — the leaves of the main axis 

 begin to disorganize. The young shoots retain their greenness through the winter, 

 remaining in a quiescent state meanwhile, and produce the main axis of the new plant 

 the following spring. When these structures are transferred to aquaria, they pass 

 through a winter-rest period, a period which is less easily disturbed, however, in this 

 form of pectinatus than in others of the same species. Extreme plasticity is character- 

 istic of various portions of the runner. Fertile nodes produce either tubers direct, or 

 leafy tips, or runners, any one of which may in turn produce a runner. The tip of a 

 secondary runner may produce a leafy shoot (fig. 53), and a tuber, instead of elongating 

 its axis in the natural way, may develop precociously a reserve bud which produces 

 the leafy stolon (fig. 54). 



As in pectinatus generally, the detached sprays of the gigantic form show a greater 

 tendency to produce tubers than the attached ones. Likewise the runner is the im- 

 portant structure which bears them. Such tubers may become very numerous. As 

 many as 15 have been counted on a single plant (fig. 62). Detached portions of the 

 plant bearing tubers float away in the drift, from whence they may or may not find a 

 favorable place of growth in the spring. The tuber-bearing runners developed at the 

 bases of the stems rarely become loosened from the tangle of vegetation at the bottom 

 and must therefore repopulate the area year after year, encroaching but slowly on the 

 surrounding region. 



