24 EXGLISn BOTANY, 



seen. Rare, and local in Ireland, where it occurs about Limerick, 

 Dublin, Westmeatb, and Mullingar. 



England, Scotland, Ireland. Perennial. Flowers not known in 

 Britain. 



Fronds ^ to f inch across, more orbicular than many of the pre- 

 ceding species, bright green above, generally purple beneath, with a 

 tuft of numerous roots from a point towards the base of the frond, 

 from which point radiate a number of veins containing spiral fibres. 

 The flowers have never occurred in Britain or France, and seem to be 

 very little known. Reichenbach figures them as coming from the 

 upper side of the frond. Lamarck, who is probably right, represents 

 them as produced from a lateral cleft near the base. Both these figures 

 have been copied on our Plate MCCCXGVII. 



Greater Duckweed. 

 Frencli, Leniicule d plusieurs racines. German, Vielwurzelige Wasserlmse. 



Section V.— WOLFFIA. EorM. 



Fronds floating, herbaceous, not tailed, wholly destitute of root- 

 fibres, and furnished with a membranous-edged basal cleft from which 

 the young frond is produced, which remains sessile and attached for a 

 short time to the parent frond; cells of the epidermis bounded by 

 straight lines. Flowers fi-om a pit on the upper surface of the frond. 

 Ovary containing a single erect ovule. Fruit indehiscent, 1-seeded. 



SPECIES v.— LEMNA ARRHIZA. Lmn. 



Plate MCCCXCVm. 



Eekh. Ic. Fl. Germ, et Helv. Vol. VH. Tab. XIV. Fig. 14. 

 Sillof, Fl. Gall, et Germ. Exsicc. No. 3478. 



Wolffia arrhiza, Wimm. Goss. & Germ. Fl. de Par. ed. ii. p. 716. Wehvitsch in See- 

 viann's Journ. Bot. 18G5, p. 113. Trimen in Seeinann's Joum. Bot. 1866, p. 220. 

 Wolffia Michelii, ScMeid. Beitr. z. Bot. Vol. I. p. 233. 

 Brtmiera vivipara, FrancJiet, in Billotia, Vol. I. p. 25. 



Fronds opaque, floating, cylindrico-conves above, and more so be- 

 neath, oval-oblong, entire, not apiculate or tailed at the base, destitute 

 of roots; the under side with spongy tissue. Young fronds solitary 

 and sessile from the very base of the parent frond. 



Discovered in a pond near the railway station at Staines, Middlesex, 

 by Dr. H. Trimen, in June, 1866, and afterwards near Walthamstow, 

 Essex, by Mr. Traherne Moggridge. 



England. Perennial. Flowers unknown in Britain. 



Fronds very minute, ^q inch long by about half as broad, differing 

 from all the other species in having no roots, and the bud bursting 

 from the base of the parent frond. 



