236 INTEODUCTION TO CEYPTOGAMIG BOTANY. 



the substance on which they grow, and not from the surround- 

 ing air or water, hke AlgsB. It is true, indeed, that a few 

 Algse, such as Botrydium, do probably imbibe something from 

 the soil by means of their rootlets, which can scarcely be mere 

 holdfasts ; but still that does not affect the general fact of 

 Algse being only false parasites. In the same manner, when 

 we examine Fungi more closely, we shall have reason to be- 

 lieve that there are exceptions there also, as to their deriving 

 nutriment from their matrix. I have, for instance, found a 

 Cyphella on the hardest gravel stones, where the fine myceli- 

 oid threads, by which it was attached, could not possibly derive 

 any nutriment, except from matters conveyed to it by the air 

 or falling moisture ; a species of jEthalium* was found on 

 iron by Schweinitz, which had been subjected to a red heat a 

 short time before ; Mr. Ivor found a Bidymium. on a leaden 

 cistern at Kew, and from the indifference which the Myxo- 

 gastric Fungi in general show, as regards the objects on which 

 they grow, it is very probable that a large portion of them are 

 dependent entirely on matters contained ia the air, and in 

 consequence that many are essentially meteoric. It cannot be 

 supposed that Spumaria derives anything from the blades of 

 grass to which it is attached, or which it involves in its pro- 

 gress, after the same fashion that the twigs of trees or annual 

 vegetables are surrounded by the growing pileus of the cortical 

 Polypori. 



* The account given by Schweinitz is as follows : " A blacksmith at 

 Salem, by no means void of sense or cultivation, had tirown on one 

 side a piece of iron which he had just taken from the fire, being called 

 off to some other business. On his return in the morning, he was 

 astonished to see on this very piece, lying over the water in his smith's 

 trough, a quantity of this fungus. He immediately sent for Schweinitz, 

 without moving anything from its place, who was equally astonished 

 to find a distinct species of ^thcdium. The mass of Fungi was two feet 

 in length, consisting of a series of many confluent individuals. It had 

 crept from the iron to some adjacent wood ; and not, as might be ob- 

 jected, from the wood to the iron. The immense mass had grown in the 

 space of twelve hours.'' I have myself seen a specimen of this fungus, 

 which Schweinitz calls JEthalium ferrincola. It has some resemblance 

 to Reticularia umbrina. The spores are precisely the same size -!- of 



-^ -^ J 4U00 



an inch, but the structure is rather that of JEthalium. 



