546 
CIX. ALISMACEiE 
numerous, small, free, arranged in a ring ; stigmas terminal ; ovules 
single. Fruit a ring of achenes surrounded by the persistent, outer 
perianth-segments. 
In ditches and ponds, below 4500 ft. ; June-September. — Lower Himalaya. 
— N. and S. temperate regions (Britain, Water Plantain). 
A. reniforme is common in the plains, and may perhaps occur in the hills 
below 3000 ft. ; it has orbicular, cordate or kidney-shaped leaves and only 5-8 
achenes forming an irregular head, not in a ring. 
CX. NAIADACEAi 
Water-plants, entirely submerged or the upper leaves floating; 
stems branching, usually long and slender. Leaves undivided, 
sheathing at the base or provided with sheathing stipules. Flowers 
small or minute, usually green, 1- or 2-sexual, on stalked, axillary 
spikes or sessile and solitary or clustered in the leaf-axils. Perianth 
of 4 scale-like segments or tubular or none. Stamens 1 or 4. 
Ovary of 4 distinct carpels each with a single ovule and a separate 
stigma or of a single carpel with 1 ovule and 3 stigmas. Fruit of 
1-seeded drupelets or achenes. — Spread over temperate and tropical 
regions, in the sea as well as in fresh water. 
Flowers in stalked spikes 1. Potamogeton. 
Flowers sessile in the leaf-axils. 
Leaves entire ......... 2. Zannichellia. 
Leaves variously toothed 3. Naias. 
1. POTAMOGETON. From the Greek potamos, a river, and 
geiton, a neighbour, referring to the usual habitat of the plants. — 
Spread over nearly the whole world. 
Water-plants, submerged or the upper leaves floating; root- 
stock creeping ; stems long, usually forking. Leaves stipulate, 
often translucent, alternate or the upper ones opposite, stalked or 
sessile, entire or finely toothed. Flowers small, 2-sexual, in stalked, 
axillary spikes rising above the water. Perianth hypogynous ; 
segments 4, concave, green. Anthers 4, sessile on the perianth- 
segments. Ovary of 4 distinct, sessile, 1 -celled, 1-ovuled carpels, 
each with a nearly sessile stigma. Drupelets small, more or less 
beaked, becoming dry and seed-like. 
Though the flowers of Potamogeton are 2-sexual, the pistil usually matures 
before the anthers of the same flower are ripe and self-fertilisation therefore 
rarely occurs. The plants are dependent on the wind for the transference of 
the pollen. P. crisjgus produces in the autumn thick shoots which are detached 
from the stem, sink to the bottom and pass the winter in the mud, safe from 
the frost, reproducing the plant in the following spring. See- Kerner’s Nat. 
Hist, of Plants, i. 552, ii. 739, and Muller’s Fertilisation of Flowers, p. 567. 
