f98 



FORMATION OF THE WINTER LEAF BUD. 



there is no perspiration worthy being so called. But I re* 

 turn to my subject. 

 Sendee oft he ^~ m ' e tne upper andunder cuticles are growing, the edge 



Tw© «orts of 



.•djeofthe 



of the leaf is completing ; the bubbles generally divide, and 



partly dry up, and horny points appear in their stead. When 

 this is complete, the leaves burst from the bud ; but there 

 are few that will not show for a long time the manner of their 

 formation; the planes for more than a month remain coveiv 

 ed with the ends of vessels, some attached to the leaf, some 

 loose: and most leaves have a bunch of vessels fastened at 

 the outside to the corner of each side rib. 



The vessels of the leaves (I mean those confined with- 

 in the midribs and side ribs of the leaf) are of two sorts; 

 the spiral and nourishing vessels. The spiral vessel is that 

 corkscrew wire, that surrounds the two last rows of the sap 

 vessels (as I shall show when I describe the division into which 

 the stem should, / conceive be separated). The nourishing 

 vessels are the only part formed of the wood, and convey the 

 sap necessary for the support of the leaf, and run on each 

 side of the spiral ones; which are generally divided into 

 little bundles of 3, 5, or 7 sets. It is impossible for any de- 

 lineation to be more exact, than that given in the Phil.Trans. 

 by Mr. Knight, of the entrance of these vessels into the midt 

 rih of the leaf. That these spirals vessels are the cause of 

 motion in leaves, and that they are perfectly solid and inca- 

 pable of carrying moisture, I hope to prove in my next letter. 

 Many leaves have a number of hairs fastened to the under 

 cuticle of the leaf, aud some to the upper. On the latter 

 they appear designed to divide the rain drop to the size. of the 

 pore it is fitted for, and those at the back of the leaf seem 

 intended to guard it from moisture, that the wet might 

 not prevent the entrance of the carbonic gas at night; 

 which it probably would do, without this precaution, 

 by resting on the apertures. But it is watching nature in 

 Why leare* ner natural state, that her laws are to be understood. , When 

 ulm/iTtVthe tne w * na * hlows with violence, the leaves turn their backs to 

 *aa. the wind; and when the sun shines, they present their 



face to it : guarding by the first means the oxigen from dis- 

 persing) and in the latter case procuring a greater quantity, 



Motive -tes- 

 te is. 



Use of the 

 hairs on leaves 



from the heat -of the sun shining on the leaves. 



W T hen the 

 leaves 



