368 General Notes. [June, 
the Linnean Society of London. The plant on which his observations 
were made was chiefly the feather-grass, Stipa pennata, but the same 
phenomena exist in many grasses, in Anemone montana, and in some of 
the Geraniacew. The essential points of structure common to all these 
self-burying seeds are: (1) a sharp point more or less covered with re- 
flexed hairs ; (2) a strong woody awn sharply bent at one point so as to 
be divided into a lower vertical and an upper more or less horizontal 
part, the vertical part being strongly twisted on its own axis (or form- 
ing a helix as in the Geraniacew). The hygroscopic phenomena exhib- 
ited by all the seeds are, (1.) On being wetted the vertical part of the 
awn untwists, and causes the straight horizontal part to revolve and 
describe a circle in a horizontal plane; the angle between the vertical 
and horizontal parts also gradually disappears, and the awn becomes 
straight. (2.) As the awn becomes dry again, the movements just de- 
scribed are reversed, the angular bend and the torsion of the lower part 
of the awn appearing. The process by which the seed of Stipa buries 
itself is as follows: the long feathery horizontal part of the awn is 
easily entangled in low vegetation, and the seed is thus held in a more 
or less vertical position, its point resting on the ground. When the 
awn becomes wet it tends to untwist, but the horizontal part being un- 
able to revolve, the rotation is transferred to the seed; the tendency of 
the seed to straighten itself is also converted into pressure of the point 
of the seed against the soil. As the awn dries again, the seed is not 
pulled out of the ground, as would be the natural result of the reversal 
of the movements by which it was buried. On the contrary, it is act- 
ually thrust deeper into the soil during the process of drying. By the 
combination of these two alternate actions the seed is completely buried. 
What special advantage it may be to a plant that its seeds should be 
buried is uncertain; in the case of Stipa, at least, it seems to have no 
connection with germination; it is conjectured that it may serve as à 
protection against graminivorous birds, etc. The explanations given by 
Hildebrand of the twist in the awn of the wild oat, and by Hanstein of 
the torsion of the awn of Erodium, appear to be inadequate to explain 
the phenomena. The hygroscopic torsion of the awn appears really to 
depend on the power of torsion residing in the individual cells of which 
the awn is composed. Thus when an isolated cell is dried it twists on 
its own axis in precisely the same manner and direction as the awn it- 
self; and just as the latter untwists in moisture, so do the individual 
cells in like condition. It is demonstrable that the torsion of the sepa- 
rate cells must cause the awn to twist as a whole. This remarkable 
power appears to depend on the molecular structure (stratification and 
striation) of the walls of the twisting cells. Although it was previously 
nown from the researches of Nägeli and others, that certain cells be- 
come twisted in drying, yet their combination so as to produce torsion 
in a considerable mass of tissue has not before been observed. Neither 
