60 CLASS TETRANDRIA. 



with spiny tubercles, and possess leaves which gen- 

 erally grow together at their base, and so become 

 perfoliate, or with the stem passing, as it were, through 

 the centre of the united leaf. The flowers are pro- 

 duced in dense cylindric heads, have an involucrum or 

 common calyx of many slender and almost bristly leaves, 

 and also a proper, superior, or crowning calyx, of a 

 single, funnel-formed piece ; the corolla (usually pale 

 pink) is superior, and tubular, spreading out above 

 into a four-cleft border ; a single seed, as in the syn- 

 genesious plants, is produced at the base of the co- 

 rolla ; and the common conic receptacle is provided 

 with narrow, bristly leaves, which are straight in the 

 wild Teasel (Dipsacus silvestris), but hooked in the 

 cultivated species {Dipsacus fullonuni), avid it is for 

 this little accident of difference in the termination of 

 these minute receptacular leaves, that the plant is 

 generally cultivated ; their curved points, arranged in 

 rows, answering inimitably the purpose of a most 

 delicate card for fine woolen cloth. 



The Scabious of the gardens, of which the brown- 

 flowered species (Scabiosa atro purpurea) is the most 

 common, differs from the Teasel, in possessing a 

 double calyx to each floret, one above, and the other 

 below the seed. 



To this artificial class, though to a very different 

 natural order, belongs the common Button-bush, or 

 Cephalanthus, so common in swamps, and along the 

 margins of ponds. It is a shrub, bearing, in July 

 and August, a profusion of perfectly globular heads 

 of flowers, each head made up of numerous florets, 

 without any general calyx or involucrum, though fur- 

 nished with minute four-cleft calyces to each floret ; 

 the corolla is tubular and slender, with a four-cleft 

 border ; the style is exerted or stretched out greatly 

 beyond the corolla, and the stigma globular ; to the 



