INTRODUCTION. 33 



plants. Wheat is an instance of the former, on the 

 ears of which the anthers may be seen, in the summer, 

 like pieces of yellow dust. The farmer calls these the 

 bloom, and when heavy rains fall at the time they are 

 upon the ears, they are washed to the ground, and 

 in consequence, many of the grains never come to 

 maturity, but remain empty husks. Fine sunny 

 weather appears to be the best for this operation of 

 nature, as it expands the grains of pollen, and causes 

 them to float, and also to burst when they come in 

 contact with the pistils, which is also a necessary part 

 of their economy. The filbert or haze 1 is an instance 

 of two sets of flowers upon the same plant. Those 

 that are to produce the pollen make their appearance 

 in the latter part of the season, while those from 

 which the nuts are to be produced, do not appear 

 till the spring following. The willow, the hop, and 

 the juniper, are instances of the two on different 

 plants. 



The volatile or floating nature of the pollen per^ 

 forms among plants an operation which, from expe- 

 rience, mankind have found to be very advantageous, 

 not only with cultivated vegetables, but with domestic 

 animals. It has been found that if the same vegetable 

 be cultivated on the same field, or the same flock 

 continued on the same pasture, for a number of suc- 

 cessive crops or generations, their quality degenerates ; 

 and if continued long enough, they would die out. 

 Something of the same kind happens to the human 

 race ; for there are many well-authenticated instances 

 where, in consequence of a few families intermarrying 

 only with each other, both the bodies and minds of 



