NOTES AND EXHIBITS. 499 



when soaked in water, as would portions of algal fronds; and 

 whicli, when examined under fairly high powers of the micro- 

 scope, agree absolutely in dimensions and structure with the 

 fibrovascular bundles of the leaf -sheaths of Posidonia australis. 

 In this plant the submerged old stems are covered with long 

 loose filaments, which are the stout vascular bundles of the leaf- 

 sheaths, persistent long after the parenchyma has decayed away. 

 These bundles are much stouter than those of the leaves proper, 

 and are the only ones found in the Sea Balls. Even the leaves, 

 however, of Posidonia are exceedingl}^ tough and durable, and 

 are found heaped up in banks in places along the sandy shores. 

 Maceration, including boiling, tried for three weeks failed to 

 separate the bundles. The source of the fibre of the Balls was 

 detected by Mr. Betche, who examined similar structures from 

 South Australia. The Port Stephens material is identical with 

 that of these. It is remarkable that in the specimens examined 

 there was no sign of a foreign nucleus, and that they were free 

 from inclusions of sand-grains. When cut through, no grit was 

 felt by the knife. Mr. Halligan sent up a fragment of Champia, 

 a glutinous seaweed which grows in moss-like clumps, amongst 

 the fronds of which were entangled some of the fibres. In rough 

 weather these clumps were noticed floating rather abundantly in 

 the waves. Supposing the fibres also, probably in numbers 

 together, to be floating, the Ohampia, and possibly some other 

 algse, would serve as a nucleus around which the flbres would 

 gather. The rough and tumble of the waves seems to account for 

 the felting, and the soft alga in the midst easily and soon decaying, 

 the felt then becomes continuous. The fibre-masses sink at once 

 in fresh water, but they are light and buoyant enough to be kept 

 rolling an indefinite time in tidal currents. It seems plain that 

 they cannot be formed by rolling on the sandy beaches, for the 

 mesh work is so close that sand-grains once enveloped could not 

 be worked out, even if the ball worked out to sea again. The 

 j)uzzle in the matter seems to be the liberation of the fibres 

 from the stems, wiiich usually grow at some length, though in 

 Port Stephens there are stretches of mud which come near to the 



