3 H Yapp . — Fruit-dispersal in Adenostemma viscosum. 
fully described this hygroscopic tissue in the Compositae, so that my results 
merely confirm their more extended observations. Hirsch 1 states that 
though in the majority of cases movement is effected by a pulvinus 
(‘ Polstergewebe yet in a few instances it is brought about by special 
motor cells in the basal parts of the hairs themselves. 
Two kinds of hairs are found on the corolla ; glandular capitate hairs, 
which occur only on the lower part, and long filamentous hairs, which are 
confined to the upper region, just below the corolla-lobes (Fig. 4). This 
second type of hair is not found elsewhere on the plant. In the bud, the 
florets are so close to each other, that the growth of these long filamentous 
hairs, during their development, results in those of one corolla being 
entangled with those of all the adjacent corollas. A dense felt of inter- 
woven hairs is thus formed, which effectually ties together all the corollas 
of one capitulum (Figs. 1 and 2). The falling of the corollas en masse , 
which is the result of their being bound together in this manner, is probably 
of considerable importance ; for if they fell separately, there would be a risk 
of some corollas being caught by the secretion of the pappus, and so im- 
peding the action of the latter in respect to passing animals. 
Hooker 2 noticed that the corollas fall off in a mass in some species of 
Adenostemma , but attributed this to their adhering together by their viscid 
surface. In this I think he was mistaken, as the lower parts of the corollas, 
which alone could be reached by the secretion of the hairs, are invariably 
free from each other (Fig. 2). Other species of Adenostemma have similar 
filamentous hairs on their corollas 3 , which probably serve the same purpose. 
In Taraxacum officinale and some other Composites, the corollas 
tend to fall, after withering, more or less in one mass. In these cases, 
however, the corollas merely adhere slightly to one another during drying, 
or at most are entangled by their ligulate tips. 
Not only are the corollas bound together, but special arrangements 
exist, by means of which both they and the styles are cut off from the ripe 
fruits, and the latter are separated from the torus. In each case, during 
the ripening of the fruit, the walls of certain cells become thick and woody. 
This serves to give a special rigidity to these parts of the flower or fruit, 
while the adjacent parts, whose cell-walls remain thin and delicate, are 
easily ruptured. The direction of rupture is determined by the relative 
positions of the hard and soft tissues. 
Thus in the corolla, a cylindrical mechanical layer is formed, by the 
thickening of the outer epidermis of the whole of its lower part. A few 
cells of the calyx-ring just below the corolla also become thickened. 
Abscission is then effected by the rupture of the thin-walled cells at the 
extreme base of the corolla (Fig. 10). Similarly the epidermis of the lower 
1 Hirsch, loc. cit., p. 38. 2 W. J. Hooker, leones Plantarum, 1840, vol. iii, tab. 239. 
3 See figures in Martius and Ejchler, Flora Brasiliensis, 18573-6, vol. vi, Part II, t. 51 and 52. 
