DUCKWEED FAMILY. 



5. Lemna gibba L. Gibbous Duckweed. 

 (Fig. 889.) 



Lanna gibba, L. Sp. PI. 970. 1753. 



Thallus slightly uiisynunetrical, obovate or short -chorale, 

 i , "-3" long, thickish or more or less strongly gibbous bei 

 neath, short-stalked when young, soon separating, provided 

 with stomata which are sparse beneath, obscurely 3-5-11.-: 

 rootcap mostly short-pointed, rarely long-pointed or obtuse- 

 fruit symmetrical; seed thick, deeply and unequally ribbed. 



In ponds and rivers, Nebraska, Texas, Ari/.ma .! i. ,1,1. .rnU 

 Also in Mexico, Europe, Asia, Africa and Au>tialia. Jim. 



3. WOLFFIA Horkel; Schkid. 



13 ; v s, } . , 



Thallus small, globose, ovoid-oblong, subcylindric or irregular, rootle, nrroln* ( 

 leafless. The vegetative growth is from a cleft near one end of the pUnt. the brmarb brim 

 mostly sessile and soon detached. The ovary contains one orthotropow orule. Fniit ipilM 

 ical or short ovate, smooth. Kndosperm in a single layer. [Name in honor of N.ih M.i 



v. \Volff, 1724-1784, Polish physician and naturalist.] 



A genus of 12 species mostly in tropical and subm-im.,! rt^m*. The following MM! two 

 Mexican species, [V. lingulata and //'. K ladiala, comprise all th- .. rnrrtctt fora* 



i. Wolffia Columbi^kna Kar- mbia 



WoltTia. i \ : \K. \ 



ll'olff'ia Columbian* K . ; ^tt^ ty. 



Thallus spherical or subellipsotdal loog. wiih 



a limited number of stomata i to 6 , looely cellular od 

 clear green throughout, not dotted nor gibbon*. 



Floating as tiiinuU .rain* )tt*t U-ncath lh> 



face of the water in stai;:-. .nt t -n.l, pool* ad ttttllam 

 Ontario to Connecticut Jcnu-y wrt to MmanoU 



and Missouri, south to I.oui->um.i 

 America. June July. 



2. Wolffia Brasiliensis Wedd. Bra/.il 

 Wolffia. (Fig. 891.) 



// 'nlffia Brasiliensis Wedd. Ann. Sci. Nat. ( III. ) 12: 170. 1849. 



Thallus oblong, smaller than the last, %"-]^" long, 

 flattish, densely cellular, with numerous stomata and 

 dark green above, gibbous, more loosely cellular, with 

 fewer stomata and paler beneath; brown-dotted through- 

 out with minute pigment cells. 



Floating on the surface of stagnant waters. Ontario. Con 

 necticut to New Jersey, west to Minnesota and Missouri, 

 south to Louisiana. Also in Brazil. June-July. 



Family n. MAYACACEAE Walp. Ann. ;,: 

 MAYACA FAMILY. 



Slender branching aquatic moss-like herbs, with linear ^ 

 soft leaves, notched at the apex. Flowers .solitary, pedtmcb 

 and regular, the peduncles bracted at the basv. Perianth 

 of 3 lanceolate green herbaceous sepals and 3 obovate \ 

 Stamens 3, hypogynous, alternate with the petals; 



24 



