INTRODUCTION TO CRYPTOGAMIC BOTANY. 419 



the student who wishes to attain correct views as to species; 

 and at the same time he must be equally on his guard against 

 changes in the fruit which might easily deceive. The different 

 varieties, for instance, of Leptogium bullatum present apo- 

 thecia both with and entirely destitute of a margin. The 

 structure of the thallus* itself requires more extensive com- 

 parative study than it has received at present, especially as 

 regards the mode of production of gonidia. On all these 

 points the introductory remarks of Fries in his Lichenographia 

 Europsea, should be thoroughly examined, though implicit 

 faith must not be reposed in every view put forth in that work 

 regarding species. 



460. No plants are more easily collected and preserved than 

 Lichens, with the exception of the rock species, of which it is 

 not always easy to secure good specimens. Capt. Carmichael 

 used to gum a piece of paper to specimens which he wished 

 to detach from the surface of rocks which it was impossible to 

 break, and then shave them off with a knife, leaving them 

 attached to the paper ; the specimen was then glued down, 

 and the upper paper removed by damping. Such a plan could 

 only be followed where a person has a tolerably permanent 

 residence, and the specimens are liable to injury from being 

 impregnated with the gum. When once dried, Lichens are less 

 subject to injury from insects than most other plants ; but I 

 have known them completely decomposed when in a constantly 

 damp atmosphere. 



46 L It is a convenient thing to have sections of cellular 



* If the structure of the thallus were more completely ascertained, 

 there would be less difficulty in deciding upon the true nature of Coc- 

 cocarpia. In C. incisa and smaragdina, I find scarcely anything which 

 can be called medullary tissue, at least agreeing with that in other 

 Lichens. The gonidia, moreover, are the eudochromes of cells lying 

 between the hypothallus and cortical stratum, and not distinct free 

 cells. In the latter, as represented in the Floi'a of New Zealand, I find 

 gonidia underlying the tissue which supports the hjinenium. The 

 thallus is, in fact, so different from that of other Lichens, that at 

 present I am constrained to consider it as part of the same organism 

 with the apothecia. I have represented the structure as I find it in 

 the latter species, at Fig. 87, h. 



