258 Eexcerpta Botanica. 
the internal substance presses against some point of the wall, 
rends it, and issues forth bent and folded upon itself. In this 
case, the emission of one of the tubes is frequently inde- 
pendent of that of the other. 
The same phenomenon may be observed in Trichocline, 
Euryops lateriflorus, and Mesogramma. In this latter plant, 
the central line of each division of the corolla (considered as 
a nervure by DeCandolle), is formed by a series of utricules 
enclosing a red resinous substance, which is also found in the 
leaflets of the involucrum. 
In Doria cluytiefolia the pericarp is covered with extremely 
fine, subulate, silvery-white hairs, which, when examined 
under the microscope, exactly resemble a thread of silk from 
the cocoon, viz. two tubes united to each other and curved 
upon themselves by desiccation. When moistened, they 
project outwards, as in the preceding case, two very fine tubes, 
which exhibit similar characters to those mentioned above. 
As these hairs are of considerable length, it is not difficult to 
cut them into pieces, and thus see the internal substance 
escape at the two extremities in opposite directions. These 
hairs are formed by two navicular valves applied together by 
their edges like those of a shell, and are destitute of a parti- 
tion, as is ascertained by the examination of the transverse 
section, or by observing the hairs of Oligothrix gracilis, 
D.C. or those of Mesogramma, which occupy the angles of the 
fruit, and are of the form of small clubs. When moistened, 
they instantaneously open, not only at their upper extremity, 
but by separating throughout their whole length into two 
transparent colourless valves which continue united at the 
base, and eject two oblong, free, mucilaginous, striated bodies, 
which subsequently elongate, and sometimes present im the 
course of their spiral certain irregular, linear, yellowish trans- 
parent fragments, which however do not turn blue on the- 
application of iodine, as has been likewise remarked of similar 
ones which escape from the utricules of the pericarp of Dra- 
cocephalum Moldavica. 
In order to ascertain the structure of these hairs, it is ex- 
pedient to examine them when the fruit is almost perfectly 
matured. 
These hairs, in certain species, occupy a determinate situa- 
tion, and those of the pappus to which they approximate do 
not participate in their characters, nor do the cellules of the 
epidermis itself, contiguous to those which produce these 
hairs, offer anything analogous in their organisation. 
The two tribes of Composite in which these hairs have been 
hitherto observed are the Ladiatifiore and the Senecionidee. 
