228 IMPERFECT PLANTS. 



of pollen, and in the shields or targets, Fig. 122, he 

 found a number of oval bodies, arranged in perpen- 

 dicular columns, which were regarded as seeds. But 

 Gaertner maintains, that these substances are a peculiar 

 kind of gem, which he denominates propago, and de- 

 scribes as being '• simple gems without leaves, or re- 

 gular form, sometimes naked, and sometimes covered 

 with an envelope, which separating at length from the 

 parent plant," are dispersed like seeds. Gaertners 

 views of the subject are most probably correct. 



Lichens are described by Acharius as forming a natu- 

 ral order, distinct from the other imperfect plants ; in 

 which the whole body performs the functions of an uni- 

 versal receptacle or thalhts, of various shapes, without 

 distinct root or stem, and furnished with vegetative or- 

 gans, by which the 6pecies is propagated. These or- 

 gans abound in the substance and on the surface of the 

 flowers, being sometimes scattered and sometimes col- 

 lected in nests, and existing in a separate organ (apo- 

 fhecium) Fig. 122, which he regarded as a partial re- 

 ceptacle, and to which other writers have applied the 

 terms saucer, shield, and cup. 



" The aquatic or submersed Jllgce form a distinct and 

 peculiar tribe. Some of them abound in fresh water, 

 others in the sea, and hence the latter have been de- 

 nominated sea-weeds The chief genera are Ulva, 

 well defined by its seed organs being dispersed un- 

 der the cuticle throughout the membranous or gelati- 

 nous substance of the frond ; Fucus, whose seeds are 

 collected together in tubercles, or swellings of various 

 forms and sizes ; and Conferva, commonly known by its 

 capillary and jointed frond. They are in general mere- 

 ly fixed by the roots, their nourishment being imbibed 



