38 GENERAL BOTANY 



distichous and corresponds to the bifarious arrange- 

 ment in opposite leaves. 



In CYPERUS, CAREX, and all others of that family, 

 the leaves are in three rows, and if one looks down 

 on the top of a plant (e.g. of the common CYPERUS 

 BULBOSUS, or the Papyrus) the leaves appear as in 

 a spiral, one edge of each at the base being covered 

 by, and the other edge covering, the leaf next above 

 and below. And if starting with any leaf, we take 

 them in ascending order, we find that the third leaf 

 after the one we started with stands exactly over 

 the latter, and the sixth again over both, and the 

 ninth, twelfth, and so on. 



In passing round the axis, therefore, we pass through 

 three leaves, or each is separated from the one next 

 above or below by one-third of a circle. Now on every 

 plant with alternate leaves, the leaves are arranged in 

 some sort of spiral, and in the case of PAN DAN US, the 

 screw-pine, they give a twisted appearance to the axis. 

 On some plants it is a two-fifths spiral, that is, on 

 going from a leaf to the one exactly above it, we 

 should have to pass five leaves, and wind twice 

 round the axis. Another common arrangement is the 

 three-eighths spiral, in which we must pass three 

 times round the axis, and take eight leaves on the 

 way, before coming to one that is exactly above 

 the first. This we find in LINUM USITATISSIMUM, 

 the Flax plant. There are other spirals with higher 

 numbers which can be easily determined by careful 

 examination. 



2. We learnt in chapter iii that the work of the 

 leaves is chiefly to assimilate carbon from the air, and 



