268 BULLETIN OF THE BUREAU OF FISHERIES. 



ranked arrangement, forming large, broad, flat sprays of foliage, which often cover the 

 bottom in large patches. It is the rarest of all Potamogetons to fruit, at least in the 

 situations where it was observed, but because of the tendency to branch profusely 

 propagation is readily effected. The branches, especially those whose internodes remain 

 short, become thickened and hardened through the storage of starch, and when 

 detached function as propagative structures. This enlargement and induration may 

 occur also at various points along the main axis that bears the propagative branches, 

 so that the final dismemberment of the whole plant provides enormous possibilities 

 in the multiplication of the species. Dismemberment may occur in the autumn, but 

 the plant is hardy, and this natural separation of parts may be deferred till spring, 

 then long rootlets develop at the nodes and establish the plant at once. The plant is 

 tardy in beginning its growth in the spring, but this tardiness in growth is obviously 

 advantageous to a plant that propagates mainly by vegetative means in the manner 

 of this species. Moreover, a very material advantage accrues in that the full and 

 complete foliage of this Potamogeton appears late in the season when many other 

 aquatics, including Potamogetons, show signs of decay. ' Growth occurs during the 

 winter. It is not great, however, and manifests itself only in a slight elongation of the 

 branches, producing fresh, green tips of foliage, which are foraged upon by aquatic 

 herbivores almost as fast as the leaves appear. 



SUMMARY OF CULTURAL FEATURES. 



The Potamogetons which yield important forage products fall into two groups: 

 Those which produce abundant herbage in their leaves — P. amcricanus, ampUjolins, 

 perfoliatus, crispus, and Robbinsii — and those which develop a large supply of starchy 

 food products in the tubers and tuberous rootstocks — P. pectinatus, filiformis, and 

 heterophyllus. 



The species which grow best in the currents of streams are P. amcricanus and 

 ohtiisifolius ; in deep water, P. pectinatus, especially the slender and gigantic forms of 

 Dudley; in calcareous regions, P. heterophyllus and filiformis; in exsiccated places, 

 P. heterophyllus. 



The species appearing early in the spring are P. amcricanus, zosferif alius, pectinatus, 

 heterophyllus, crispus, and amplifolius; those growing late in the autumn and continu- 

 ing throughout the winter are P. crispus, amplifolius , and Robbinsii. 



Abundant fruit is produced in P. perfoliatus, obtusifolius, and filiformis, and on 

 pectinatus in most situations. Vegetative reproduction occurs freely in all species. 

 The important vegetative structures are: Winter buds or hibernacula in P. obtusifolius 

 and zosterif alius; modified branches in P. crispus and Robbinsii; tubers in P. pecti- 

 natus and filiformis; tuberous rootstocks in P. heterophyllus, and subterranean buds in 

 P. americanus, amplifolius, and perfoliatus. 



NATURAL AND ARTIFICIAL PROPAGATION. 



The natural propagation of Potamogetons has been touched upon in a general survey 

 of life conditions, and it has been seen that these plants propagate freely by means of 

 various vegetative structures. At this point it is desirable to consider this method of 

 propagation in greater detail, and to present data which will afford a means of com- 

 parison between the general seed habit and the tendency to produce vegetative propa- 

 gative structures. 



