12 CLASS-BOOK OF BOTANY. 
turn round these, and thus coil themselves firmly on to this 
support. It would be quite easy for you to prove this fact of 
the irritability of the petioles for yourself if you had a young 
plant of Clematis in a pot Im the house or in a greenhouse; 
but the experiment is not one which could be satisfactorily 
demonstrated to a class, so you must accept the statement 
regarding it on the authority of those who have conducted. 
this and similar experiments. 
Observe the handsome flowers and their arrangement. 
They do not stand singly on their stalks, but are produced in 
large branching clusters towards the ends of the stems. These 
clusters spring from the axils of the upper leaves. Notice that 
at a distance of about an inch from the main leaf-axil in which 
it stands it bears a pair of very short rudimentary leaves, 
from the axil of each of which springs a slender flower-stem. 
This generally bears another pair of rudimentary leaves, and 
ends in a single flower; and this process is repeated to the 
extremity of the cluster. The main stem of the cluster is 
here called the peduncle; the secondary stems, bearing the 
individual flowers, are pedicels; the rudimentary leaves on 
the flower-stems are bracts; wlule the whole cluster or 
inflorescence is said to be a cymose panicle. (The mean- 
ing of this term will be more readily comprehended later.) 
You will find that the bracts repeat the same arrangement as 
the ordinary leaves—viz., they are in opposite pairs, and the 
pairs are at right angles to each other, so that from their 
position and arrangement we believe they are derived from 
foliage-leaves. What, then, is the explanation of their rudi- 
mentary condition? It is probably this: that as the flowers 
depend largely for the conveyance of their pollen to the 
stigmas upon insects, it is essential that they should be as 
conspicuous as possible; and this is attained in this way, 
among others—by the leaves in whose axils they stand bemg 
reduced to the very smallest size, so that it is only by their 
position that we know they represent leayes at all. (In some 
species of Clematis you will find the clusters are almost 
reduced to solitary flowers.) 
The flowers when fully open vary from 14in. to nearly 4in. 
in diameter. Note the outer whorl of 6 (sometimes 7 or 8) 
white sepals, which are free (aposepalous) and attached below 
all the other whorls (inferior). On the outside they are covered 
with a fine down, or pubescence (hence they are said to be 
pubescent), which also covers the pedicels and bracts; on 
the inside they are of a pure shining-white, or in the smaller 
forms of a greenish-white. In the buds these sepals are 
placed edge to edge, and this form of exstivation is called 
valvate. Note the total absence of petals, the sepals acting 
both as covering and attractive organs. (From their resem- 
