102 



The Naturalist. 



both for and against the theory that Lichens are Ascomycetous Fungi 

 parasitic on algse, since 1868, when Schwendener formally stated it, 

 and I for one am not disposed to dogmatise upon the subject. But 

 this I must say, that the more I see of their structure and morphology, 

 and the more closely I observe the different stages of their develop- 

 ment under ordinary and natural conditions, on old walls, gates, the 

 trunks of trees, &c., the more does the theory appear to me to harmo- 

 nise with the facts. In like manner the researches that have been 

 undertaken during the last few years, with a view to demonstrate the 

 truth or falsity of the theory, appear to me to leave a clear balance in 

 its favour. But this is by the way. Let us turn to what more imme- 

 diately concerns us, and consider the nature of the process by which 

 their sexual reproduction is brought about. 



Our knowledge of this phase of their life history is at present of a 

 very limited character, but the investigations of Stahl* leave little 

 doubt that, like their congeners among the true Fungi, they are 

 propagated in this, as well as in an asexual manner. 



In the thallus of every Lichen it is usually possible to distinguish 

 two elements, the characters and relative proportions of which differ 

 in different genera, and even in different species. One of these 

 consists of green cells, the so-called Gonidia, which in many cases are 

 identical with free-living algge, while the other is made up of a 

 number of colourless cellular threads or hyphse, whose morphological 

 and physiological characters are in the main identical with those of 

 Fungi. The best known reproductive structures are usually spoken of 

 as Ajjotjiecia and Sjpermogonia. The apotJ/ecia are similar in almost 

 every detail to the cup-shaped receptacles of the Biscomycetee already 

 described. They are composed of a number of clavate spore-bearing 

 asci, intermingled with which are delicate filaments swollen at the 

 tip — the paraphyses. They commonly differ in colour from the 

 thallus on which they are borne. The Spermogonia are small cavities 

 of various shapes in the upper surface of the thallus, which produce 

 very small spore-like bodies called spermatia. 



The "apothecia" of Lichens bearing such a strong resemblance, ■ 

 both in outward appearance and internal structure to those of Fungi, 

 the idea naturally suggests itself that they may have a similar origin. 

 The results of the investigations of Stahl, mentioned above, enable us 

 to assert that at least there is some evidence for the belief that they 

 have. 



* An excellent resume of these investigations from tlie pen of my able friend, Mr. 

 S. H. Vines, M.A., of Cambridge, may be read in the Quarterly Journal of 

 Microscopical Science for October, 1878. 



