258 



Excerpta 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 cluyticefolia 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 in 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 Labiatiflorce and the Senecionidea. 



