GC) SUMMARY OF CURRENT RESEARCHES RELATING TO 



different level from the others ; when the number is four, they are 

 arranged in two opposite pairs at different levels. Instead of a single 

 tigellum, there are often two of equal size, united in growth during 

 the greater part of their lengtlj, but distinct towards the base. One 

 of these axes occupies the normal position, the other being applied to 

 it laterally. 



The appendage is undoubtedly a reserve of food-material. When 

 a seed possessing it germinates, it is exposed along with the radicular 

 extremity, increases for some time after the rupture of the testa, then 

 gradually loses its starch, which it gives up to the embryo, and finally 

 dries up and perishes. 



Resistance of Seeds to extreme Cold.* — E. Wartmann has ex- 

 posed fresh-gathered Spanish chestnuts for nearly two hours to a cold 

 of at least — 110°, derived from a mixture of sulphuric ether and solid 

 carbonic acid, each seed being carefully wrapped in thin tinfoil, so as 

 to prevent the surface coming into contact with the ether. The chest- 

 nuts were then planted in the soil ; they germinated and developed in 

 every respect as successfully as those which had not been exposed to 

 the cold. The power of resistance to extreme cold appears, indeed, to 

 be a very general property of seeds. 



Mechanical Contrivances for the Dispersion of Seeds and 

 Fruits.j — A. Zimmermaun has subjected to a fresh examination the 

 structure of the seed-vessels of Gramine^e, Papilionacete, and Gera- 

 niaceae, by the torsion of which the seeds are buried in the soil, 

 especially in relation to the alternate turgidity and desiccation of the 

 tissues. His conclusions, which are mainly in accord with those of 

 C. and F. Darwin, are as follows : — 



1. The hygroscopic torsion of the awns of Gramineas is the result 

 of the effort after torsion of the outer cells of the stereome, and of the 

 strong contraction of its inner cells, which probably assist by the 

 fact that when they swell they assume an oblique position. The 

 micella of the former cells are arranged in spiral lines, those of the 

 latter in oblique rings. 



2. The effort after torsion of a single spirally striated cell is 

 caused by unequal intensity of swelling and unequal firmness in the 

 direction of the two systems of rows of micella. The swelling of an 

 imaginary cylinder without thickness causes in general a torsion in 

 the direction in which there is the strongest swelling. The radial 

 swelling of a cylinder possessing thickness, causes, when it is strongest, 

 a torsion in its outermost layers in the direction of less firmness ; in 

 the inner layers, one in an opposite direction. The most probable 

 explanation of the fact that a cell in which the most strongly marked 

 striations and pores are arranged in spirals inclined obliquely to the 

 left, turns itself to the right when it swells, to the left when it dries 

 up, is that on the one hand the swelling is strongest in a direction 

 vertical to these striations and to that of the pores; on the other 



* Arch. Sci. Phys. et Nat., v. (1881) p. 343. See Naturforscher, xiv. (1881) 

 p. 276. 



t Pringsheim's Jahrb, wiss. Bot., xii. (1881) pp. 542-77 (3 pis.). 



