282 MONOCOTYLEDONES. 



has a convex receptacle, carpels many, united and capitate. 

 Damasonium. Sagittaria (Arrow-head) has monoecious flowers, 

 several whorls of stamens and spirally-arranged achenes on a very- 

 convex receptacle. S. aagittifolia reproduces by tuberous buds formed at 

 the end of long, submerged branches. The leaves, in deep and rapidly running 

 water, are long and strap-shaped, but in the air arrow-shaped. 



Honey is secreted in the flower and pollination effected by insects. Alisma 

 plantago has 12 nectaries. The submerged flowers of Elisma natans remain 

 closed and are self-pollinated. Butomus has protandrous flowers. There are 

 about 50 species, which mostly grow outside the Tropics. Uses insignificant. 

 The rhizome of some is farinaceous. 



Order 6. Hydrocharitaceae. This order differs chiefly from 

 the preceding in its epigynous flowers. These are in general uni- 

 sexual (dioecious), and surrounded by a 2-leaved or bi-partite 

 xpathe ; they are 3-merous in all whorls, but the number of whorls 

 is generally greater than 5, sometimes even indefinite. The peri- 

 anth is divided into calyx and corolla. The ovary is unilocular with 

 parietal placentation, or more or less incompletely plurilocular. The 

 fruit is berry-like, but usually ruptures irregularly when ripe. Em- 

 bryo straight. Most often submerged water-plants, leaves seldom 

 floating on the surface. Axillary scales (squamulw intravaginales). 



Hydrocharis. Floating water-plants with round cordate leaves ; 

 S3, P3 (folded in the bud); -flowers : 3 (-more) flowers inside 

 each spathe ; stamens 9-15, the most internal sterile. ? -flowers 

 solitary ; three staminodes ; ovary 6-locular, with many ovules 

 attached to the septa ; styles 6, short, bifid. [The petals of the 

 9 -flowers bear nectaries at the base. In this and the following 

 genus the pollination is without doubt effected by insects.] 

 H. morsus ranee (Frog-bit) has runners ; it hibernates by means of special 

 winter-buds Stratiotes ; floating plants with a rosette of linear, 

 thick, stiff leaves with spiny margin, springing from a short 

 stem, from which numerous roots descend into the mud. In- 

 florescence, perianth, and ovary nearly the same as in Hydrocharis, 

 but the ^-flower has 12 stamens in 3 whorls, of which the 

 outer 6 are in 1 whorl (dedoublement), and inside the perianth 

 in both flowers there are numerous (15-30) nectaries (stami- 

 nodes?). S. aloides (Water-soldier); in N". Ear. only ? -plants. 

 Vallisneria fpiralis is a tropical or sub -tropical plant, growing gregariously on 

 the mud in fresh water. The leaves are grass-like, and the plants dioecious ; 

 the (? -flownrs are detached from the plant, and rise to the surface of the water, 

 where they pollinate the $ -flowers. These are borne on long, spirally-twisted 

 peduncles which contract after pollination, so that the $ -flower is again drawn 

 under the water, and the fruits ripen deeply submerged. Elodea canadensis 



