236 ALG, r E, CHAP. IV. 



is indicated by the changing of the colour of the 

 tubercle to a deep brown, and their escape, by its 

 changing to black. 



Or targets. From a different part of the same plant, or from 

 a different plant of the same species, there are also 

 found to issue a number of cup-shaped or target- 

 shaped substances, sitting or supported on short 

 pedicles of the same contexture with the frond, 

 and of a sort of greenish colour, but gradually 

 becoming dark as they ripen. If one of them is 

 now divided by means of a vertical section, it will 

 be found to ce4arn immediately under the black 

 crust at the top, a number of small and egg-shaped 

 substances arranged in perpendicular columns. 

 These substances are the seeds which finally escape 

 . through the crust. In this species both the barren 

 and fertile flowers are well exemplified in Lichen 

 physcdes. (PI. VII. Fig. 12.) 



Which Such is the theory of Hedwig. But, Gaertner 

 who is also a great authority on this subject, con- 

 tends that the powdery substance, ejected from the 



gems,' and targets or saucers, consists, not of seeds, but of a 



constitut- . . 



ing a pro- peculiar species or gem, which he denominates the 

 Propago, and describes as being a simple gem with- 

 out leaves or regular shape, sometimes naked and 

 sometimes covered with an envelope, which, sepa- 

 rating at length from the parent plant, is dispersed 

 in the way of seeds, but is not itself a seed. This 

 is a subject on which it is, of course, difficult to 



7 



