CHAP. II. 
LEAVES. 
117 
Pinus pinaster, — sylvestris, — cembra, — larix, 
— microcarpa 
Betula alba and pubescens, 2 t ii — fmticosa gene- 
rally, 
Corylus avellana, /y — americana and tubulosa, in their 
male catkins. 
The whole of this curious question has been simplified by 
Professor Henslow, in observations printed for private cir- 
culation ; and I am happy to be able, by the permission of 
their author, to lay them in this place before the public. 
54 
The scales on a cone of the Spruce Fir {Abies excelsa) are 
placed spirally round the axis, at equal intervals ; and after 
eight coils of the spiral, the twenty-second scale ranges verti- 
cally over the first. If this arrangement be referred to a 
cylinder, and then projected on a plane cutting its axis at 
I 3 
