DISPERSAL BY WATER. 



845 



suppose thcat rain-water running off the plants and then trickling along the ground 

 would be a very efFectual means of dispersing fruits and seeds, but closer observa- 

 tion convinces one that distribution is comparatively seldom effected in this manner, 

 and that wherever such dispersion does occur it is invariably supplemented by 

 some other means of dissemination. The best-known instances are afforded by two 

 plants which, on account of their extraordinary properties, were brought to Europe 

 from the East by pilgrims and crusaders in the Middle Ages. They were called 

 " Roses of Jericho", and all sorts of marvellous tales were told concerning them. One 

 of these plants is Anastatica Hierochuntica, a Crucifer which grows on the Steppe- 

 lands of Egypt, Arabia, and Syria, and which has the peculiarity that its branches 



Fig. 463. — Fruits which open upou being wetted witli water. 



J Anastatica Hierochuntica, dry. 2 The same when wetted, s Fruit of Mesenibryanthemum Candollcanum, dry. •• The same 

 when wetted. ^ Fruit of Mesembryanthemum annuum, dry. «The same after being wetted. 



curve inwards when the fruits are ripe in such a manner as to form a trellis round 

 the closed, pear-shaped siliquas, which are very numerous and are situated at the 

 extremities of the ramifications, and to protect them from being touched (see fig. 

 463 ^). The shape of the structure in this condition is something like that of an 

 unopened rose, and it remains unaltered so long as it keeps dry. When moistened 

 the branches at once open back and stretch straight out (see fig. 463 ^). The fruits 

 also open at the same time, and the seeds are then liable to be washed out of the 

 fruit- valves by falling rain. When growing wild Anastatica remains closed during 

 the long drought which follows the maturation of the fruits, and it is not till the 

 winter rains set in that the tangle of branches opens and the seeds are waslied out 

 of the fruits. The second "Rose of Jericho", Asteriscus pygnuMUS, is a small plant 

 of the Composite family, and ranges from the northern portion of the Sahara to 

 Palestine, being met with in especial abundance in the neighbourhood of Jericho. 

 In this case the branches do not close together when the fruits arrive at maturity, 

 but the involucral leaves, which are arranged in a rosette, close up over the capitula 



