Sunshine, Rain, and Wind 



which one can only realise the perfection after very careful 

 microscopic dissection, and by much constructive imagi- 

 nation. But it is unfortunately impossible to describe 

 either the difficult chemistry of wood and cellulose, or 

 the mechanical beauty of the tracheid. 



One other little point should be mentioned in this 

 chapter, for it is but seldom noticed anywhere. 



The stems of most herbs and shrubs are not either 

 straight or cylindrical. There is usually a zigzag curva- 

 ture and a system of indistinct grooves and ridges. 

 Where the leaf joins the stem there is often a bold 

 sweeping curve at the leaf base, continued as a faint 

 elevation down the stem. Where leaves are opposite, 

 a ridge joins the bases and is often artistically set off 

 by a pallisade of hairs. Leaf veins are often sunk below 

 the surface, and lead down to intricate little hollows, 

 where the bud is nestling between leaf and stem. 



These sculpturings and ornaments are regulated by 

 three distinct and different governing principles. There 

 is (i) the mechanical support of the stems, and also (2) 

 the protection of the young bud in the hollow or axilla 

 of the leaf (the " oxter," as it is called in Scotland, is 

 exactly like the bud axil of many leaves). But there is 

 also (3) another intention, which is to utilise rain and 

 atmospheric dust. The importance of dust has not been 

 realised until quite recently. 



The researches of Mr. Aitken in this country have 

 shown that even on the summit of Ben Nevis it is very 

 difficult to get a sample of air with only one dust particle 

 per cubic centimetre (.061 cubic inch). When Pasteur, 

 on 20th Sept. i860, attempted to get a sample of germ- 

 free air at the Montanvert near Chamonix, he had to 

 raise his flask above his head to get rid of body currents 

 and breath, then by careful manipulation break off the 

 point of the flask, which was then hermetically sealed by 



191 



