INTRODUCTION TO CRYPTOGAMIC BOTANY. 377 



and Kiitzing may teach us much as to the early stages of these 

 plants, but their conclusions must be received with the greatest 

 caution. Indeed, it is sometimes difficult to know what au- 

 thors mean, Agardh, for instance, when he asserts so posi- 

 tively that the tissues of Phcenogams are true Gonfervce, only 

 means that they are homologous ; and so again when he talks 

 of the conversion of animals into Algje, or the contrary ; or 

 when again he speaks of other supposed metamorphoses of 

 Algte, he does not mean what the words imply, for in other 

 places he declares expressly that the changes of Algae into 

 Lichens are mere assumptions by the Alga3 of Lichenoid 

 forms. 



413. The forms assumed by Lichens are extremely various, 

 though there is in general great similarity of fruit. Even 

 in the same genus the most different habits prevail, and, as has 

 been seen before, the same species can assume very various 

 forms under differing circumstances, so that two states may 

 even be occasionally considered as belonging to different genera. 

 This does not, however, always prove that the genera are badly 

 founded, but that the^ species are not well circumscribed. 

 Fries has done a great deal towards the reduction of anomalous 

 forms to their true originals ; and if he has sometimes gone too 

 far, and has not attended sufficiently to characters afforded by 

 the fruit, he has still done good service to the cause ; and, not- 

 withstanding the labours of Montague, a similar reform is 

 wanted amongst exotic species. 



414. Those Lichens which are nearest to Fungi — namely, the 

 VerTUcarice — have so little crust, that they are not always 

 easily to be distinguished. The Verrucarice, however, grow 

 very commonly on living bark, a very rare circumstance 

 amongst true Fungi. Still, at some stage of growth a myce- 

 lium or obscure crust may be traced ; and, indeed, it is self-evi- 

 dent that it must exist, as, without a medullary substance no 

 perithecia or asci could be produced. It must be remembered, 

 too, that the perithecia are not produced singly, but in a com- 

 mon mass, and there must, therefore, be a common mycelium. 

 This, however, may traverse the young tissues of the bark 

 without producing any cortical stratum, and will be recognised 



