FAMILIES OF FLOWEE^^Xx PLANTS. 



19 



parted perianth. 'I'lio ovary is coiujxtscMl of scNctal distinct carjuds 

 which become small stone fruits or nutlets. A curious featuic of the 

 |)ondweeds, particularly in J*<ii<ini<i<j< fan . is tlic diU'crcnci' in shape often 

 exhibited between the inunersed leaves and those that tloat on the sur- 

 face of the water. Thus I\ Sj,l,ulhis has its I'loatini:- IcaNcs o\al or 

 elli[)tieaK while its sul)niersed leaves are narrowly linear: this peculiar- 

 ity is the result of the i)lant"s adaptation to the conditions undci- whii-h 

 it iTi'ows, the exposure to air anil siuditrht tendinu' to the production of 

 expanded Idades. In species which ijrow wholly suhmeroed there is 

 no (lit!erence in the sha[)e of the leaves. (See Fi<i-. 14.) The 'genus 

 AjxuKx/ffoii, coin})osed of about lo Old AN'orld species, contains some 

 beautiful ornamenttil acjuatics, known as lattice-jjlants on aecoinit of 

 the o})en lacedike tissues of their leaves, which a]>pear as if pierced 

 by many holes. 



Family Scheuchzeriaceae. — (Juneaiiinaceae). Arrow-grass laniily. 

 Four genera and only about LO species, of wide distribution. All are 

 Jiiarsh plants, with rush-like or sedgedike leaves and small perfect 

 flowers born in spikes or racenjcs. The ])erianth is in two series, thus 

 showinir traces of diti'erentiation into a calyx and corolla: the ovarv is 

 composed of several car])els, slightly 

 united. y)-i(jl()rlihi , the best known 

 iienus. with three North American 

 species, is found in salt marshes along 

 the coast and in alkaline situations in 

 the interior of the continent, its small 

 greenish spike and linear or filiform 

 leaves being quite inconspicuous. 



Family Alismaceae. — Water- Plan- 

 tain Family. Thirteen genera and 

 about 65 species, widely distributed in 

 .fresh water swamps. The plants are 

 herbs with long petioled leaves and 

 scapose flowers borne in liroad panicles 

 or racemes. The flowers vary greatly 

 in structure, being perfect, monoecious 

 or dioecious: but tliey are always borne 

 in whorls on the peduncle, and })Ossess 

 a perianth, usually in two distinct 

 series. The ovaries are often numerous, each carpel becoming a small 



Flc. 1.1.- Arum-lt'aved arrowbead (sa- 

 fiittaria (irijUIUi) showing whole plan I 

 reduced with enlarged fruit and siameu. 

 (After Britton and Brown, HI. Fl. 

 North. U. S.) 



