CHAP. II. 
LEAVES. 
97 
is also eight. The position of the several beginnings of the 8 
spirals (viz. on Nos. 1. to 8.) is shown in C; and in D we 
have the numbers (169. 106. 43. &c.) which respectively 
begin the second series of each spiral. 
To discover the primary spiral, we may fix on any scale 
as a point of departure (No. 1.), and then, by numbering the 
scales on two of the secondary spirals (as 1. 9. 17. &c. and 
1. 6. 11. &c.) which proceed in opposite directions, we may 
afterwards very readily place the numbers on all the scales. 
The easiest method of obtaining the common differences (viz. 
8 and 5), for the purpose of numbering the scales in the two 
cases selected, is to draw^ a circle round the cone, and count 
the number of each of the two kinds of spirals intersecting it 
(which will be 8 of the first and 5 of the second). When a 
secondary spiral perfects a complete coil (as 1. 9. &c. 161. 
169.), the number of the spirals of the same kind is readily 
seen; but the former mode for obtaining this number will 
apply equally well to cases where the cone is too short for the 
coils to be completed." 
In their normal state leaves are obviously distinct, both from 
each other and from the stem. But, in some cases, adhesions 
of various kinds occur, and give them a new character. Thus, 
in Cardui, and many other thistle-like plants, the elongated 
bases of the leaves adhere to the stem, and become what is 
called decurrent. In Bupleurum perforatum the lobes of the 
base of the leaf not only cohere with the stem, but, projecting 
beyond it, grow together, so as to resemble a leaf through 
which the stem has pierced: this is called being perfoliate. 
Frequently two opposite leaves grow together at the base, as 
in Caprifolium perfoliatum ; to this modification the latter 
term is often also applied, but that of connate is what more 
properly belongs to it. 
The anatomical structure of the leaf is this : — From the 
medul'ary sheath diverges a bundle of woody tissue, accom- 
panied by spiral vessels : this passes through the bai'k, and 
proceeds, at an angle more or less acute, to a determinate 
distance from the stem, branching off at intervals, and, by 
numerous ramifications, forming a kind of network. At tiie 
point of the stem whence the bundle of fibro-vascular tissue 
H 
