TRANSACTIONS OF SECTION K. 



853 



The surface of the fruit or seed in actual contact with the glass at the moment 

 ■sv^hen hreakinof occurs is generally very small. In order to find the pressure per 

 square inch this surface was measured, and its area calculated in the following 

 manner. An object-glass was painted with a thin layer of black paint, and 

 pressed down upon tJie seed. That part which was in contact was of cour.ee 

 covered by the paint ; a piece of white cardboard was then pre.ssed down over the 

 seed under glass, and the area of the stain on the cardboard was calculated by the 

 help of a glass slide ruled in lOOths of an inch. It was found that the pressure 

 in pounds to the square inch was as follows : — 



In the Cabbage seed 

 ,, Hemp seed. 

 ,, Euonymus europfeus 



about 106-2 lb. to square inch. 

 „ 433-5 lb. „ 



„ 244 lb. 



But of course a square inch of surface is never called into action under natural 

 conditions. 



The resisting power depends chiefly upon the shape of the seed and the 

 character of the sclerenchymatous tissue. Generally speaking, the curve of the 

 transverse section of a seed shows an unmistakable resemblance to that of an 

 ordinary stonebridge. On the other hand, both the longitudinal vertical section 

 when the seed is lying a flat surface in a natin\il position) and the longitudinal 

 horizontal section are generally lanceolate to ovate in shape. These latter curves 

 are probably of great importance, but for a diflerent purpose. It was found, e.(/., 

 difficult if not impossible to exevt .sufficient pressure on the seeds of orange and 

 Abrus precatorius, even when two surfaces of wood were employed to hold them, 

 the shape and the slippery or smooth coats of the seeds resulting in the seed 

 springing out and jumping off". It is possible to make orange seeds, e.ff., jump 

 fifteen feet along a flat surface by a slight blow on the end. This peculiar shape 

 will probably enable the seeds to escape from tlie teeth of an animal, or perhaps 

 facilitate their passage through the alimentary tract. Some of the curves of the 

 seeds employed are ilustrated in the paper. 



Many special peculiarities of fruits and seeds are important aids to their 

 resisting power. In particular, the ridges on the cremocarps of Myrrbis and 

 Carraway, the peculiar three-cornered nut of Beechmast, the spongy pericarp of 

 Tropffiolum, very greatly diminish any danger of injury by pressure from above, 

 as they yield to the pressure and do not break. When seeds are lying on bare 

 earth they are often simply pressed into the earth if any pressure is exerted upon 

 them. Thus, e.ff., four seeds of Hemp were placed upon a layer of earth only a 

 quarter of an inch deep, which was spread upon a glass plate. A weight of 

 56 lb. placed gently on these .seeds simpty buried them in the earth without 

 injuring them in any way. 



1901. 3 K 



