28 INSECT TRANSFORMATIONS. 



by Priestley, Ingenhouz, and Ellis, and had been 

 mistaken by Linnaeus for a crop of byssi, ascertain- 

 ed beyond question that it always consisted of the 

 minute buds of common mosses, such as the wall 

 screw rnoss ( Tortula muralis) and the common hair- 

 hood moss (Polytrichum commune) * At Glasgow, 

 we have repeatedly remarked, that on the walls of 

 houses, built with freestone raised from a quarry more 

 than a hundred feet under the surface of the soil, 

 the whole exterior would, in the course of one month, 

 appear as green as if painted, with these innumera- 

 ble germinating mosses. "f 



The germination of mosses on walls appears to 

 arise from the seeds (sporules) being carried into the 

 air. This process is facilitated by their extreme 

 minuteness and their comparative lightness, for they 

 do not sink in water like the seeds of phenogamous 

 plants and the eggs of insects, as appears from their 

 germinating on the surface of stagnant water as fre- 

 quently as on walls. In low situations, the mode in 

 which the seeds of cryptogamic plants are diffused 

 is well exemplified in the puff-ball (Lycoperdon), 

 which, when ripe, explodes its sporules in the form 

 of a smoke-like cloud. Mosses again, which grow 

 on trees and walls, if they do not thus explode their 

 sporules, must drop them into the air; and, as they 

 chiefly ripen early in spring, the winds which then 

 prevail will scatter them to considerable distances. 

 .But we only state this as a highly probable inference 

 from Drummond's discovery: to detect these all but 

 invisible seeds floating in the atmosphere, and trace 

 them in their passage from the parent plant to the wall 

 or tree where they begin to germinate, we" think is 

 hardly possible. 



If the doctrine be sound, that every plant arises 

 from seed, we must either believe that innumerable 



*Linn. Trans. t J. R. 



