812 THE DISTRIBUTION OF SPECIES BY OFFSHOOTS. 



fact that this vegetable structure grew and developed (although only in isolated 

 patches and principally as crusts on stones) in the immediate neighbourhood of the 

 spots where they collected it, we need not be surprised at the conclusion of our own 

 peasants who thought the tubers of the Lesser Celandine had fallen with the rain 

 from heaven. It should be mentioned that the manna sent to the Israelites on 

 their journey out of Egypt to the Holy Land is identical with the Lichen described 

 here and figured on page 695, and the older view that the manna of the desert 

 was the sap of a Tamarisk {Tamarix gallica inannifera) exuded under the influence 

 of a parasite is without any foundation. 



Spores take the first place among the reproductive bodies which are distributed 

 by wind. Many Ascomycetes develop some of their spores by abstriction from the 

 free ends of special hyphss. These rise up into the air from the substratum, which 

 is permeated or covered by the mycelium. In this way the separated but loosely- 

 adhering spores can be carried away by the slightest atmospheric movement. In 

 the Moulds known as Aspergillus and Penicillium, whole series of spores are cut 

 ofi" from the end of each hypha (see figs. 193 *> ^' ^- ^, p. 18), and as they are crowded 

 closely together a single breeze carries oiF innumerable quantities of spores. By 

 breathing only lightly on the small forest-like colonies of supports the spores are 

 whirled as dust into the air, and as they are extremely light they not only remain a 

 long time suspended in it, but even in perfectly still air are carried sometimes up, 

 sometimes down, by the currents due to slight diflferences of temperature, again 

 being carried horizontally or whirled along until at last they settle, and become the 

 starting-point of a new Mould formation. The spores abstricted from the ends of 

 the so-called sterigmata in the Hymenomycetes (see figs. 389 and 390 ') may also be 

 detached and carried away by wind, but apparently most of the spores in these 

 Fungi separate spontaneously in calm air and fall to the ground, covering it with a 

 delicate layer of dust, to be afterwards carried away from this resting-place by 

 breezes. 



The spores of Ustilaginese and those in the Eecidia of Uredinese (see p. 686) are 

 at first covered with delicate membranes and sometimes inclosed in special receptacles. 

 As soon as they are mature they form a powdery mass, which bursts through the 

 covering membrane, and the now exposed spores are blown away as dust by the 

 wind. If they have developed in deep receptacles shaking is necessary before they 

 can be blown away. The spores then fall from the mouth of the receptacle into the 

 currents of air. In many Myxomycetes and Gasteromycetes (see fig. 367 \ p. 618, 

 and fig. 391 ^ p. 690) delicate twisted threads called the capillitium are developed 

 simultaneously with the spores. The web of threads with the spores between them 

 is inclosed in a membrane (see fig. 449 1), When this membrane bursts at maturity 

 and the receptacle is thrown open only the spores in the immediate neighbourhood 

 of the opening can be blown away by the wind, the deeper ones being held back by 

 the capillitium. The lower layers of the capillitium are then raised by tha action 

 of dry winds, and thus quantities of new spores are continually carried from below 

 up to the opening. In this way it happens that the spores of these plants are only 



