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POTATO MURRAIN. A formidable 

 disease in potatos, which appeared first in 

 this country in the year 1845, but was pre- 

 viously known in America. It is charac- 

 terised by the rapid putrescence of the 

 leaves and haulm, which is first indicated 

 by the presence of a little mould, Pero- 

 nospora infestans, which preys upon the 

 tissues, spreading rapidly in every direc- 

 tion. The tubers also exhibit brown spots 

 on their surface and within their tissue, 

 and, according to circumstances, decay 

 with greater or less rapidity. It is now 

 admitted by most persons that the mould 

 is the primary cause, but as it attacks the 

 tissues before it appears externally it is 

 almost impossible to apply a remedy. 

 Many plans have been adopted, but the 

 two most important, though far from in- 

 fallible, are powdering the sets well with 



I flower of sulphur ; and early planting, 

 with the removal of the haulm as soon as 

 the mould appears. The disease has been 



! equally bad in the wettest and hottest sea- 

 sons, and has baffled the researches of all 

 practical and scientific men. It was in 

 many districts as bad in 1860 as it was on 

 its first appearance— the worst year per- 

 haps being 1846, when its sudden inroad 

 produced a fearful famine in Ireland, which 



! resulted in the loss by death of thousands ; 

 and, as good often comes out of evil, it 

 also led to the repeal of the Corn Laws. 



German authors distinguish two forms, 

 the wet and dry rot. It is, however, to be 

 observed that these diseases, which are 

 characterised not only by the peculiar con- 

 dition of the tubers, but by the presence 

 of Fusisporium Solani tubcrosi, were pre- 

 valent in this country before 1845 ; the 

 brown mottled appearance of the tubers, 

 and the presence of Peronospora on the 

 leaves and the exposed tissues, being pre- 

 viously unknown. [M. J. B.] 



POTEL^E. (Fr.) Hyoscyamus niger. 



POTEXTILLA. A genus of shrubby or 

 | herbaceous plants belonging to the Eo- 

 j sacecp., and allied to the Strawberry, from 

 which they are mainly distinguished by 

 having their seeds in a dry not pulpy 

 receptacle. The British species of most 

 frequent occurrence are P. Fragariastrum, 

 a humble hedge plant, with ternate leaves 

 j made conspicuous in early spring by its 

 small white flowers, which are often mis- 

 taken for those of the Wild Strawberry ; 

 P. anserlna, the Silver "Weed, a roadside 

 plant well marked by its pinnate leaves, 

 glossy with white silky down, and large 

 yellow flowers ; P. reptans, distinguished 

 by its slender creeping ' runners,' quinate 

 leaves, and large yellow flowers ; and P. 

 Tormentilla, a humble slender trailing 

 plant, of which the lower leaves are qui- 

 nate, the upper ternate, and the flowers, 

 which are yellow, have four or five petals. 

 P.fruticosa has pinnate leaves and yellow 

 flowers ; it grows in bushy places in the 

 North, but is rare. Many species are cul- 

 tivated, of which P. nepalensis, airo-san- 

 gv.inea, Thomasii, and h&matochrus have 

 furnished varieties of all shades of purple 



and crimson. French: Quintefeuille ; Ger- 

 man : Filnffingerkraut. [C. A. J.] 



POTERIUM. A genus of Rosacea; named 

 from the Latin poterium, a * drinking cup, 1 

 as its herbage, which has much the flavour 

 of cucumber, was employed in the old 

 English drink known as a cooi tankard. Its 

 flowers are monoecious, its separated male 

 and female florets being compounded into 

 more or less compact heads, from which 

 depend little tassel-like bunches of bright- 

 pink stamens. Of this plant the botanist 

 recognises two forms, probably only varie- 

 ties :— P. Sanguisorba, the Lesser Burnet, 

 which has an angular stem about a foot 

 high, pinnate leaves with serrated leaflets, 

 and seeds somewhat acutely quadrangular : 

 this occurs in calcareous soil ; and P. muri- 

 catum, the whole plant of which is much 

 larger than the preceding, the seeds four- 

 winged, and more or less pitted with raised 

 tooth-like elevations. The latter seems 

 to be apparently wild in districts where 

 sainfoin has been cultivated, and is pro- 

 bably a foreign plant introduced with 

 continental seed ; or else, from agrarian 

 cultivation, burnet may have become the 

 coarse plant which farmers have lately had 

 so much reason to complain of from its be- 

 ing sown with their sainfoin. At first this 

 evil was overlooked, as the intended crop 

 only afforded a sample of the burnet here 

 and there ; and as both possessed pinnate 

 leaves, the farmer scarcely distinguished 

 them, though in the burnet the leaflets 

 are serrated, while in the sainfoin they 

 are entire at the edges. In order to distin- 

 guish the seeds of these two plants, re- 

 ference should be made to the particulars 

 given in treating of Sainfoin. [See Oxo- 

 brychis.] The colour of the seeds is a 

 light brown, and the wrinkled aspect of 

 both is so much alike that the pest is often 

 overlooked by the buyer of sainfoin-seed, 

 or we should hardly find what should be I 

 sainfoin turn out as much as fifty per cent, 

 of burnet. To prevent this the best plan 

 is to sow only decorticated seed. [J. B.] 



POTHERB, WHITE. Valerianella oli- 

 toria. 



POTHOMORPHE. A genus of Piperacew, 

 consisting of undershrubs having some- 

 what the appearance of some of the , 

 species of Pothos, whence the name. They I 

 are natives of the tropics of the Old and j 

 New World, delighting in damp shady | 

 situations. They are studded with pellucid j 

 glands, and have large membranous heart- 

 shaped sometimes peltate leaves. The 

 spikes emerge from the axils of the leaves, 

 above one or two branches, that proceed 

 from the same spot. The stipules are 

 small, opposite to the leaves ; the flowers 

 perfect; the fruit very small. [M. T. M.] 



POTHOS. The name of a genus of climb- 

 ing shrubs of the family Orontiacece. 

 They are natives of India, China, Mada- 

 gascar, New Holland, &c; and have for the 

 most part cord-like steins, sending out 

 false roots here and there, and attaching 

 themselves to trees. The leaves are in the 



