150 



The pores in the leaves of plants are almost innu- 

 merable. Mr. Lewenhoek found above a hundred 

 and seventy.two thousand on one side of a leaf of Box. 

 The leaves of Rue are as full of holes as a honey. comb. 

 Those of St. John's Wort likewise appear full of pin* 

 holes to the naked eye; but the places where those 

 hok's seem n> be, are really covered with a thin and 

 Mi hite membrane. Through a microscope the backside 

 of the herb Mercury looks as if rough with silver, and 

 all the ribs are full of white round" transparent balls, 

 fastened by slender stalks, Jike so many grapes. A 

 S^&e-leaf appears like a rug or shag full of tufts of 

 silver tiiri:;^!^, and embellished with round crystal 

 beads, fastened by tender footstalks. The prickles 

 of a i^tlle are formed for tcting just as the sting of 

 animals* every one of them is hoJlow, and terminates 

 in a fiue point, with an opening near its end. At the 

 bottom of each prickle lies a pellucid bag, containing 

 a clear liquor, which upon the least touching the 

 prickle, is ejected at the little out-let, and if it caters 

 the skin causes pain and inflammation by the pungency 

 of its salts. 



The leaves of plants are of great consequence to 

 their life. At these the air passes in, and goes 

 through the whole plant, and out again at the roots. 

 If the leaves have no air, the plant uill die, as is easi- 

 ly proved by the air-pump ; whereas if the leaves be 

 left on the outside of the receiver (parted by a hole ce- 

 inen-ted by wax) while t ( so have air, the plant will 

 thrive and grow, though its roots and staiks are kept 

 in vacuo. The leaves likewise chiefly perform the ne- 

 cessary work, (but w ;o can explain the manner !) of 

 altering the water received at the root, into the nature 

 of the juices of the plant. And hence it is, that the 

 life of plants depends so immediately upon their leaves. 

 The husbandman OIU-M suffers for want of this know- 

 ledge. A crop of Sdint-foin is valuable, and its roots 

 being perennial, will yield an increase for many years. 

 But it is often destroyed at first by suffering it to be 

 fed upon by sheep ; lor if they eat up all the leaves.) 



