CHAPTER II. 



STRUCTURE. 



The habits of waterlilies are too well known to need more than a brief 

 statement here. These plants are found in the shallows of slow streams or 

 still water all around the world. The long rhizomes of the Castalia group 

 creep along in or upon the mud bottom of ponds or in a tangle of vegeta- 

 tion overlying this, in a depth of water from a few centimeters to as much 

 as 5 or 6 meters, branching here and there, and dying off behind as they 

 advance by apical growth. By far the greater number, however, have an 

 erect, tuberous stem or caudex, which never acquires any considerable 

 length, but stands with its growing apex about on a level with the mud in 

 which its lower portion is buried. From the stem in every case a great 

 many stout, fibrous roots pass downward and anchor the plant in place, 

 while the leaves and flowers rise upward. The former lie flat upon the 

 water surface, the upper side being dry and exposed to the air. Under 

 some conditions the petioles may be strong enough to hold up the leaves 

 and make them totally aerial. All of the species, at certain periods of 

 growth (germination and beginning of each annual growing season), 

 produce small, thin leaves which lead a submerged existence. The flowers 

 of about half of the species open at the surface of the water and seem to 

 float upon it, those of the other half are raised on strong peduncles some 

 distance above the water level. Only in one or two species (A^. rudgeana, 

 N. amazonuni) is cleistogamy known to occur. The flowers in such cases 

 never reach the air, or only do so for a few hours, after self-pollination has 

 been effected. After anthesis the fertile flowers are drawn down into the 

 water by movements of the peduncle, and here the seeds ripen. By 

 means of a buoyant aril, the ripe seeds from the irregularly bursting fruits 

 rise to the water-surface and are floated far and wide. 



These peculiar conditions of life have impressed themselves strongly 

 upon the forms and functions of the waterlilies. Manifold adaptations 

 have arisen in every part of the plant. We shall discuss these in order 

 in the succeeding pages, taking up first the gross morphology, then the 

 finer anatomy of root, stem, leaf, and flower, and finally the physiology of 

 the genus. 



