VOL. XIX.] PHILOSOPHICAL TRANSACTIONS. 125 



part be narcotic, for example, the whey may not be so ; or the one may be 

 hurtful, and the other a good and useful medicament. 



Tragopogon flore luteo, J. B. yields a juice, which on the first springing 

 from the wound is white and thick, but immediately it turns yellow, and then 

 redder and redder; it is of no unpleasant taste: it is something glutinous and 

 very oily, and parts not with much, if any whey, and therefore it is easily formed 

 into cakes alone. Convolvulus major, J. B. bleeds freely a white and very sharp 

 juice; not only the stalk and leaves, but the white flowers also in proportion, 

 bleed as plentifully as any other part. 



There is another very clammy juice, which is of a golden or yellow colour, 

 upon drawing ; this is from the seed vessels of centaurium luteum perfoliatum, 

 C. B. in July, and after; even when the seeds therein contained are turned black 

 and ripe, they yield plentifully and freely enough. It is liquid on first drawing, 

 and after a while it thickens, parting with no whey ; and this is of the colour of 

 amber: it sticks to one's fingers, and draws out into threads like bird-lime; it 

 would never become harder than very soft wax, and that by being dried in the 

 shade only ; for if ever so little exposed to the heat of the sun and fire, it soon 

 became exceedingly soft. But as for the cakes made up of it and wheat flour, 

 in winter they became very hard and firm, but the unmixed cakes still soft. 

 These burn with no unpleasant smell; they emit a lasting flame ; they still keep 

 their amber colour; and draw out in threads in burning, like wax. To this 

 last coagulate and clammy juice, and which will not much harden, may be 

 added the yellow juice, which the wounds of Angelica sativa Park, yield ; it 

 will not harden by insolation or long keeping ; yet it stiflens, and will draw into 

 threads. 



The next sort of coagulate and clammy juices noticed, are gums; and 

 some of them seem to remain long liquid : he has not tried if they are inflam- 

 mable : there are others which grow hard, and are certainly not to be kindled 

 into a flame. They are easily dissolved in water, and sparkle when put into a 

 flame; which two natures argue a serous or waterish part in them : again, put 

 into a flame, they melt, and become as it were liquitl and ductile; which shows 

 the caseous part in them ; and because they will not flame, it is an argument of 

 their leanness and scarcity of oil. All three put together plainly evince gums to 

 be coagulate juices. 



The next instances are of gums which grow hard in time, readily dissolved in 

 water, and are not to be kindled into a flame, though they become thereby soft 

 and ductile. 



The American or Indian rhubarb sown in our gardens is the only plant that 

 he has met with, or ever saw, which yielded a gum; and yet, because it is of 



