122 
ORGANOGRAPHY. 
BOOK I. 
as well as to MiquePs remark, that they never occur upon 
radical leaves (Strawberry). 
Turpin considers them of two kinds. 
1. Distinct, but rudimentary, leaves^ when they originate 
from the stem itself, as in Cinchonaceae, &c. 
2. Leaflets of a pinnated leaf, when they adhere to the leaf- 
stalk, as in Roses, &c. 
The ligula of grasses, a membranous appendage at the apex 
of their sheathing petiole, which some have considered stipules, 
should rather be understood as a membranous expansion 
analogous to the corona of some Caryophylleae, such as 
Silene. 
It has been already noted, that when they surround the 
stem of a plant they become an ochrea ; in this case their 
anterior and posterior margins are united by cohesion ; a 
property that they possess in common with all modifications 
of leaves, and of which different instances may be pointed out 
in Magnoliaceae, where the back margins only cohere, in cer- 
tain Cinchonaceae, in which the anterior margins of the stipules 
of opposite leaves are united, and in a multitude of other 
plants. 
e3. Of Bracts. 
63 66 67 
64 65 
All the parts that have hitherto been subjects of enquiry 
are called organs of vegetation ; their duty being exclusively 
to perform the nutritive parts of the vegetable economy. 
Those which are about to be mentioned are called organs of 
