10 VARIATION AND DIFFERENTIATION IN CERATOPHYLLUM. 



is absolutely no indication of root-hairs on this etiolated portion of the 

 stem. At the ends of the branches and of the main axis of normal, 

 healthy plants are found growing buds which at intervals form new 

 whorls. At the tips of the branches the internodes become progressively 

 shorter as we go towards the end, thus giving rise to the compact mass of 

 leaves at the tip of the branch which is so characteristic of Ceratophyllum. 

 The plant is monoecious, both staminate and pistillate flowers being 

 borne on the same individual. A detailed morphological study of the 

 development of the flower has been published recently by Strasburger 

 ( :02) . Reproduction is not entirely by seed, but a form of vegetative 

 multiplication occurs very frequently (cf. Schenck, '86). At the ap- 

 proach of winter the tips of branches bearing growing buds break off 

 and sink to the bottom. Since the bud is protected by the thickly 

 matted leaves of the whorls near the tip it is able to winter over in this 

 condition. With the advent of spring, growth begins again and by its 

 continuance the bud gives rise to a new plant. In the early spring 

 young plants which have been formed in this way may be found in 

 various stages of growth. When the conditions are not too severe the 

 plant as a whole winters over, renewing its growth in the spring like a 

 perennial. This fact was first noted by Irmisch ('53, p. 528), who says 

 regarding the "Dauer der Ceratophyllum-Arten:" 



Sie sind, wie ich mich iiberzeugt habe, bestimmt perennierend. Viele Examplare 

 fand ich im Friihjahr an der Spitze der deu Winter iiber frisch gebliebenen Zweige, die 

 sich nicht weiter verandert batten, weiterwachsen; in anderen Fallen waren die Blatter 

 der Zweigspitzen bogig iibereinander gekriimmt und die altern Internodien des Zweiges 

 waren abgestorben, so dass sie kleine lochere, isolirte BoUen darstellten. Auch diese 

 wuchsen im Friihjahr weiter. 



Certain of the plants (in Series V and VI) used in the present study 

 were collected in the spring after having passed the winter in this way 

 without dying or being broken up. 



• The characters of the plant with which the present study has prin- 

 cipally to do are the following: 



(1) The number of leaves in the whorl. For verbal convenience this 

 character will be referred to throughout as "leaf-number." 



(2) The position of the whorl on the plant, relative to the main axis. 



(3) The size of the various divisions of the plant, as measured by 

 the number of whorls they bear. 



(4) The position of the branches, relative to the proximal end of the 

 main axis. 



With reference to the determination and recording of these char- 

 acters the following should be said: The character "number of leaves 

 to the whorl " was easily determined for the majority of the whorls, but 



