20 BRITISH LICHENS. 



pleasant. It is with the view of helping the student over these initial 

 difficulties that the present paper has been written. 



The vegetable kingdom is divided into two great sections, the 

 Phancrogamla and the Cnjptogamia, the former possessing flowers con- 

 taining male and female organs, the latter being destitute of flowers, and 

 having their male and female organs less conspicuous or altogether con- 

 cealed within special receptacles. Lichens* belong to the section 

 Cryptogamia. They are closely related to other siib-divisions in this 

 section, viz.. Fungi and Algcc, the line of separation on either side being 

 so indistinct that it is not always easy to say where it runs. Nature, 

 indeed, has drawn no definite line even between the animal and vegetable 

 kingdoms, much less between the sub-divisions of the vegetable kingdom. 

 Notwithstanding this near approach of Lichens to Algse on the one hand, 

 and Fungi on the other, the students of each have, by mutual consent, 

 agreed to certain hmitations which serve all practical purposes. Lichens 

 oire distinguished from certain Fungi to which they have a resemblance 

 by possessing in their structure the green bodies called gonidia, of which 

 we shall have to speak at length hereafter ; from Algas they are dis- 

 tinguished by bearing reproductive spores in asci. Other points of 

 difference can only be understood by the student as he becomes more 

 fully acquainted with the subject, hence these must suffice for the 

 present. 



A perfect Lichen consists of the vegetative part called the Thallus ;t 

 and the fruit-bearing receptacles, the Apothecin,\ considered to be the 

 female organs, seated on the thallus ; with which are found associated 

 the Spermagonia% and the Pijcnides,\\ considered to be the male organs. 

 Although every Lichen should, theoretically, have these parts all present, 

 it must be understood that the thallus is often so imperfectly developed 

 that it is scarcely discernible, or, as in parasitic species, is absent, while 

 in others, though the thallus is perfectly developed, the apothecia are 

 hardly ever to be seen, and the spermagonia and pycnidia are still more 

 rarely to be found. 



We will proceed to notice these various parts more in detail, beginning 

 with 



THE THALLUS. 



I. — The thallus difl'ers much, according to the species, in form, 

 size, colour, and texture. Having regai'd to the surface on which a 

 Lichen grows, the thallus may be upright or prostrate, i.e., vertical or 

 horizontal. 



* This word, which is pronounced Likens, the ch being hard, 18 said to be 

 derived from the Greek word XetX'?*' a wart, 

 i From da\\6s a frond or green leaf. 

 t From o.Tro upon, and Otjkt] a sack. 

 § From ffirepiJ.a a seed, and yovr] generation, in allusion to their function. 



H From irvKvdrT)^, indicating many things pressed one against the other, 

 probably on account of their close growth. 



