III. THE LEAF. 6 1 



the dew of the morning, have you ever considered 

 why it is so rich upon the grass ; — why it is not upon 

 the trees ? It is partly on the trees, but yet your 

 memory of it will be always chiefly of its gleam 

 upon the lawn. On many trees you will find there 

 is none at all. I cannot follow out here the many 

 inquiries connected with this subject, but, broadly, 

 remember the branched trees are fed chiefly by 

 rain, — the unbranched ones by dew, visible or 

 invisible ; that is to say, at all events by moisture 

 which they can gather for themselves out of the 

 air ; or else by streams and springs. Hence the 

 division of the verse of the song of Moses : " My 

 doctrine shall drop as the rain ; my speech shall 

 distil as the dew : as the small rain upon the tender 

 Iierb, and as the showers upon the grass." 



23. Next, examining the direction of the veins 

 in the leaf of the alisma, b, Fig. 3, you see they 

 all open widely, as soon as they can, towards the 

 thick part of the leaf; and then taper, apparently 

 with reluctance, pushing each other outwards, to the 

 point. If the leaf were a lake of the same shape, and 

 its stem the entering river, the lines of the currents 

 passing through it would, I believe, be nearly the 

 same as that of the veins in the aquatic leaf. I 

 have not examined the fluid law accurately, and I 

 do not suppose there is more real correspondence 



