54 TKOSEKPINA. 



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 invisi- 

 ble ; 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 sinM rain upon 

 the tender herb, and as the showers upon the grass." 



23. Next, examining the direction of the veins in the 

 leaf of the alisma, , 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 than may be 

 caused by the leaf's expanding in every permitted direc- 

 tion, as the water would, with all the speed it can ; but 

 the resemblance is so close as to enable you to fasten the 

 relation of the unbranched leaves to streams more dis- 

 tinctly in your mind, just as the toss of the palm leaves 

 from their stem may, I think, in their likeness to the spring- 

 ing of a fountain, remind you of their relation to the desert, 

 and their necessity, therein, to life of man and beast. 



