The stem branches freely in sympodial fashion giving the axis 

 a zig zag look characteristic of this mode of growth. Roots are 

 developed freely at the nodes and if these touch the bottom an- 

 chor the plant as it grows forward in its inclined position in the 

 water. The leaves are grasslike with sheathing bases that clasp 

 the stem. 



Vegetative propagation is easy for w^ater plants and they 

 spread rapidly by means of rhizomes, buds, runners, etc., or by 

 simply detached branches of the plant that take root and resume 

 growth. Some of them have been known to spread in remarkable 

 way by purely vegetative means. A striking example is seen in 

 Elodea canadensis, the pistillate form of which was introduced 

 into Europe about 1836, and overran the continent, and in a 

 short time became a veritable pest in all quieter waters. Not 

 until a few years ago, however, when Dr. Strasburger introduced 

 the staminate plant of this species for experimental purposes 

 was there the possibility of seeds in this form in Europe. 



The widespread tendency of the submersed ^ngiosperms to 

 produce seeds despite their favorable opportunity for vegetative 

 multiplication emphasizes the importance of fertilization or at 

 least of seed production in higher plants. The work of Bene- 

 dict (3) indicates that the conjugation of gametes inhibits senil- 

 ity in the race and may afford distinct advantage in addition to 

 all the fine strategy of the seed as an organ for plant renewal 

 and dispersal. 



The sessile flowers of Heteranthera diibia are borne at irreg- 

 ular intervals along the stem and are intermixed with the veg- 

 etative leaves. Each flower is invested by a spathe which per- 

 sists until the seeds are well developed. The tubular perianth, 

 which is about two centimeters long, is divided into six segments 

 which in the open flower are of a pleasing yellow color and sug- 

 gest by their form the common name ''water stargrass." The 

 open flower shows a bilateral arrangement of the perianth-seg- 

 ments and this zygomorphy extends to other members of the 

 flower. The three stamens are inserted in the perianth tube 

 (Fig. 1) and show considerable difference in their structures and 

 arrangement. The single abaxial stamen rises slightly above the 

 two equal and lateral ones, and there is no stamen on the axial 

 or inner side of the flower. The three stamens represent prob- 

 ably both of the origmal two cycles of these organs. Solms- 



50 



