2 72 BULLETIN OF THE BUREAU OF FISHERIES. 



P. filiformis represents a tuber-forming species which produces these propagative 

 structures apparently in the manner of P. pectinaius. Since material was collected but 

 once during the summer, no definite data can be recorded regarding the details of tuber 

 formation beyond the fact that the plants develop from tubers, as the collected materials 

 show (fig. 36, 37), and that these tubers, whether they occur singly or in a series of 

 two or more, have a likeness to those of pectinaius, in size resembling the common form 

 and in shape approaching more nearly the deep-water form. In details of structure the 

 tubers of filiformis are similar to those of pectinaius. Judging from the general habit 

 of the plant it seems fair to assume that the tubers have arisen in the same way and that 

 vegetative propagation would depend largely upon them. 



PROPAGATION BY TUBEROUS ROOTSTOCKS. 



The vegetative structures of P. heterophyllus terrestris are illustrated in figures 10 

 and II. Morphologically they are a series of more or less shortened and hardened 

 internodes richly provisioned with starch. They are borne at the terminal portions of 

 the underground stems. Well-developed buds, the incipient, erect axes, occur at alter- 

 nate nodes of the structures, while the inter\'ening nodes remain sterile, as in the case of 

 undifferentiated rootstocks. Figure 8 represents a typical plant collected early in 

 May. At this season the plant is still submerged. The tuberous rootstock of the pre- 

 vious year sends up young, erect shoots from the fertile nodes, and extends the growth 

 horizontally by an elongation of the terminal bud to form the new rootstock. 



The underground stems acquire a distinctly tuberous appearance very early in the 

 summer. At Myers Point, where the collections were made frequently, the tuberoua 

 character became apparent at the time when drought conditions began to prevail in 

 the pools; that is, when the water level was reduced to such an extent that the sub- 

 merged, leafy shoots gav^e place to the later-formed, erect shoots topped with tufts or 

 rosettes of aerial leaves which rest upon the mud. Figure 12 represents a plant of this 

 kind. By comparing the plants shown in figures 12 and 16 the origin of the tuberous 

 rootstocks is clear. In figure 16 tuberous structures appear at the ends of the new 

 underground stems, B and C. This tendency to produce the tuberous growth may 

 appear early when the plant is still submerged, though it may be deferred till drought 

 conditions prevail, when the new type of leaves forming the rosette above the ground 

 function to produce the abundant storage of starch which is found in the mature tuberous 

 rootstocks. 



Some underground stems, throughout the growing season, continue to produce 

 internodes nontuberous in structure (fig. 9), but they are exceptional rather than the 

 rule. The tip of the rootstock that is destined to become tuberous generally shows 

 this character very early. The internodes at the end do not elongate in the usual way, 

 but appear serially in a more or less bead-like form (fig. 10 and 11). Figures 13 and 14 

 represent the tuberous rootstocks partially developed. Figure 10 shows a fully mature 

 one. These structures, and many others in similar stages of development, were col- 

 lected in July and it is interesting to note that while some are only approximately mature 

 others are fully so thus early in the season. In November all evidences of other plant 

 parts have disappeared and the tuberous rootstocks only are left isolated in the mud, 

 where they remain in a quiescent state through the winter. A typical structure, as it 



